They are community based freeware software. Gimp being similar to Photoshop and for bitmap creation / photo manipulation. Inkscape could be compared to Illustrator (but must say that if you are used to Illustrator there will be some smaller adjustment). Both of the programs are available for PC/MAC/LINUX and now Android...
In either case definitively both programs capable of the same professional results and quality as the commercial costly counterparts.
https://play.google.com/store/apps/details?id=org.gimp.inkscape