Just discovered this yesterday and just opened it quickly one time.
​It looks nice and surely interesting to check out for anyone into chiptune music making.
It is in a tracker sequencer stylelee though, so be aware if being scared of heights and only used to horizontal piano rolls! 

Ahhh...
It is also for freeee and without anal probing also known as advertisement!

Google Play:
https://play.google.com/store/apps/details?id=com.twobit.fakesid

There is no information given except this:
Fake SID is a chiptune tracker that let's you create Commodore 64 music.
But it does not seem too hard to figure out with an hour or two of exploration.

Did post about this abum but now it got a nice little review by the Cheap Bit Sid website.

To read it go here:
chipbitsid.co.uk/uncategorized/gesceap-novum/

So the Nanoloop family have a new member.
Okay so it is not Android but it is a portable and old school and funky, so felt that it had to get mentioned. Plus that an old gameboy can be had for like 10-15 moneys...
Ahh the cartridge is more expensive of course but analogue mojo with three channels for 69 moneys is more or less what other gadgets cost, like pocket operators and the like... Plus have admiration for this single developer to just keep pushing such a niche product as much as he is.

Here are some facts and link:
http://www.nanoloop.com/mono/index.html

Specs

3 channels:

r = Rectangular Wave

• Dual oscillators
  Variable pulse width
  Low-pass filter with adjustable resonance

c = Click

• Single impulses
  Extra-resonant bandpass filter for 808-like drum sounds.

n = Noise

• True analog noise generator or
  Dual square waves
  Bandpass filter with medium resonance

Technology

On the original Game Boy models, one pin of the cartridge connector functions as audio input, connected to the built-in amplifier. This unique feature allows to generate sound on the cart and play it through the headphone output on a completely analog signal path.

In the nanoloop mono cart, the analog components (op-amps, comparators, logic cells etc) of a PIC microcontroller are connected and configured in such a way that they form a hybrid soundchip with 3 analog filters and a true random noise generstor, using only a few passive external components.

Hardware

The cart is a flat but very robust PCB with all electronic parts embedded. 

Software

Nanoloop mono is a stepsequencer with per-step control for all parameters. There are 8 banks of flash memory each of which can hold 15 patterns per channel and a song structure.

Compatibility

DMG (original Game Boy) OK, clean and bassy

Game Boy Pocketworks, but less bass, more hiss, whine

Game Boy Colorworks, but very little / distorted bass, a lot of hum and whine

Game Boy Advancedoesn't work, cart won't even boot

Allthough amplitudes are the same as with internal sound, with nanoloop mono's softer characterisic, differences in audio quality are more noticeable.
Some improvement is possible by adding capacitors to the Game Boy's main board ("bass mod" and "noise filter mod"). However, GB Pocket will still produce a high-pitched whine and GB color will still hum and distort basses.

In conclusion, only the original Dot Matrix Game Boy can be recommended. 
​
Sync

Nanoloop mono offers the same sync options as nanoloop one.

8-Bit Music Theory is a Youtube channel that goes deep into music theory of 8-bit game music.
They are well made and interesting to see even if you are not interested in grating 8-bit sounds
and just want to learn some music theory, but if you want to get some authentic early video game music vibe going this is great.
Down below there are some examples but there are many more here:
​https://www.youtube.com/channel/UCeZLO2VgbZHeDcongKzzfOw

It is good to see that this is getting a small but nice update as the developer is spending a lot of time on web based audio (which is pretty cool and will write about it soon). Also gives a reason to bring this interesting application up again as it is one of the more interesting apps for Android there is. Anyone that is looking for a more advanced synthesizer engines that can sound raw should check this out. Plus that it comes with a lot of effects, a simple drum machine and four track sequencer.

Google Play:
https://play.google.com/store/apps/details?id=nl.igorski.mikrowave

As a bonus a video showing what the developer is doing when he is not coding...

Wanted to mention this for some time but kept on pushing it in hopes that I would find time to make some music with it first... but alas to no avail so better mention this now as for me this and Oscilab Pro is the two new apps that made me most excited 2015.

Bytebeat is a more or less new phenomena and have only existed for some years now. 
It is writing lines of mathematical equations that generate a chiptunish sound/noise so it is interesting as it is a way to accomplish minimal compositions in a new way. 
But think that it is a way to find inspiration for new tracks and rhythms that is hard to get in other ways and mixed in with other elements it can certainly give your tracks an edge.
There is two other Bytebeat apps on Android- Droidbeat and as a machine insert in Caustic.
All three of these apps have advantages but maybe this is the one I prefer for some reasons...
As both Droidbeat and Bytebeat Machine is for free so i suggest to download both and use as needed. Maybe I should mention as well that Caustic is for free without being able to export wav/midi but like Droidbeat it is possible to record directly into a DAW and the last session is saved. Plus that there is a fully functional version for PC... 

The Caustic version do have two engines in one instance that can be mixed together plus that it comes with sequencers and of course the possibility to use 14 of them in a composition. The presets are more meant to be used as instruments and not as whole composition but that is a small detail.

Droidbeat machine is great and it have something that the others do not have.
​It have the possibility to change the sound using four sliders. Meaning that if it is hard to write the code to get good results it is easy to use a preset and just phuck around with the sliders until something nice comes up. To be able to save directly to wav file there is a paid version but the free one saves presets and can of course be recorded directly into a DAW etc.

Bytebeat machine do have one very nice trick up its sleeve and  instead of being confined to low digital rates and bytes it is possible to use a cleaner sound setting with variations. This makes it more flexible as it can fit into mixes better depending on what you are looking for... The other advantage is that it comes with very good presets and presets with the inventor of Bytebeat!
​Just listening to them makes me inspired to start new tracks.
The Playstore page (as in this post underneath) and the app have a good explanation of how to create your own Bytebeat compositions without being to confusing. Well worth a read if you are using Caustic or Droidbeat.

There is of course also the possibility to take a equation from one app to another...
If there is someone using Bytebeat as part of a composition please send to musicalandroid@yahoo.com want to use some Bytebeat myself but never know with time etc and it would be nice to hear this utilized mixed in with other sounds...

Play Store info:

Bytebeat Machine is an experimental software synthesizer. Instead of structured composition or instruments it uses functions to generate audio in real-time.
Sometimes simple input functions contain a large amount of musical structure. Sometimes the result is unexpected.. and interesting. Or you can ignore all that and just use this app to generate bleep and glitch noises. Bytebeat Machine has several preset examples to get you started.
Features
• Free. No ads or other tracking garbage.
• Two modes: bytebeat (8-bit) and floatbeat (32-bit).
• Selectable sample rates from 8kHz to 44kHz.
• A number of preset input functions. Save your own input functions for later use.
• Custom text input mode with copy, paste, undo, mystery button (?) and more.
• Export output as .wav file.
• Various output visualizations. Yay.
• Speed slider (kind of hidden under the presets).
What is bytebeat?
Bytebeat output is fully defined by the input function. There are no pre-set instruments, samples or structures. Even slight changes in the input function produce significantly different output (as a hint, prime numbers generally result in less repetition).
Input function has a time index (t) and usually various bitwise and arithmetic operations. Input function is evaluated constantly and time index is incremented by one in each iteration.
The simplest input function is "t", which produces numbers 1, 2, 3, ... and outputs a sawtooth wave audio. Sawtooth wave is generated because the result is wrapped to 8 bits (bytebeat): 0-255 remain unchanged, but 256 becomes 1, 356 becomes 101 and so on.
Input function "t * 2" decreases the wavelength and produces a result one octave higher. Input function "t & 128" produces a square wave. Bitwise operators << and >> can be used for more interesting results. Input functions can be combined with bitwise operator "|" or even "&" and "^", for example "(t>>9) | (t>>13)".
Bytebeat Machine uses 'C -type syntax' and basic arithmetic operations, bitwise operations as well as comparisons are supported:
- arithmetic operations: +, -, *, /, %
- bitwise operations: <<, >>, &, |, ^
- comparison operations: <=, >=, ==, !=
Bytebeat was first introduced late 2011 in a blog posthttp://countercomplex.blogspot.com/2011/10/algorithmic-symphonies-from-one-line-of.html by 'viznut'. Online tools such as http://wurstcaptures.untergrund.net/music/ surfaced soon after, followed by a theoretical introduction http://countercomplex.blogspot.com/2011/10/some-deep-analysis-of-one-line-music.html and a paper http://arxiv.org/abs/1112.1368. Active community discussion and development in IRC and various forums (pouet.net) lasted a couple of months.
This app might be developed further based on interest and feedback. #bytebeat

This is an older application but it is still a very good application. Perfect for controlled chaos glitchy type of rhythms to record and reuse. It is also deeper than can be suspected at first glance. 
Android Experiments is a Google project with free experimental applications and this is the first music app on that page. Most of it being graphic  in nature. 

To see the other apps if you missed my post about this page before:
https://www.androidexperiments.com/

Just a some wave forms that goes on five tracks and in a later update (that I have not tried) there is two sample tracks added.  So if you are looking for a genuine Chiptune experience that goes back into the misty beginnings of computer music making here you have it.

Play Store info:



8Tones is an app where users can create 8-bit music/chiptune music on the go!FEATURES
• Create 8-bit music
• 5 channels (channel 0 - square 50%, channel 1 - square 25%, channel 2 - square 25%, channel 3 - triangle, channel 4 - beats/noise)
• Tracker like interface
• Customizable interface like accent colors and background

Confused? Go to this website for more info:
http://guova.weebly.com/8toneshelp.html

or simply select HELP on the main menu.

ATTENTION!
Due to very low demands and poor reception, I updated 8Tones one last time and I will not update it again. However, if this app gains more downloads I will continue support it!

How to do Chiptune music using SunVox by Florida Music Tech Program.

The sounds recorded on this website is from a company that specializes in recovering data from hard drives and they have made a fair amount of recordings of how the hard drives sounds like before they fully leave all functionality behind.
Recording by brand and with explanation of what is the problem.
So it is not a sample website and they never thought that it was going to be used for music or sound manipulation etc. meaning that you would have to record them into something else or use some kind of software to capture the sounds. It is worth it if you are into chiptune or just digital noise. Different and interesting source for your sampler!
Go here and take a listen -
http://datacent.com/hard_drive_sounds.php

This is a great twenty minute video showing off SunVox for chiptune music making by the developer himself. Highly recommended for anyone interested in making chiptune music.

Well this is great even if it is not for download.
If you have followed this website for a while you already know that I am a big fan of this documentary and did a interview with the director and a review of the film.
If not go now and check out their website and buy or see it for a small sum on their Vimeo channel...
http://europein8bits.com/

There is a lot of Nanoloop being used by the musicians (in Gameboy format) and there is a segment with the developer of Nanoloop in the film.

Okay it is not a Android app but the developer is and part of this web browser instrument can be found in his Android app - Mikrowave. ( He also made the funky controlled chaos rhythm machine Kosm). The big reason for posting this is to get the idea how to use a chiptune based sound for a live drone manipulation. It is working pretty good!

Tried this a long time ago and found it hard to get to terms with specially on a smaller screen and kind of buggy as well... but if you missed it and like trackers it is for free and without publicity. 

Play Store link:
Milkytracker