Usenti is a simple bitmap editor for paletted images, it is the result of me being completely fed up with the lack of dec^H^H^Hany palette support in Paint, and finding the bigger photo applications a little too big for comfort. The basic toolset is very similar to MS-Paint, but often less annoying. The various palette/color manipulation tools like the palette-bar palette swapper, and variable zooms and gridlines can make drawing basic things a lot easier.
The main drive for Usenti has always been for use in GBA development. As such, it has a good exporter to GBA-usable formats. The same one as in grit in fact, so I'll refer you to that for further details.
Current version: 1.7.10.