PPM is yet another Game Boy (Color) tile and map editor that uses GTK. It supports many export formats (raw binary, GBDK .c, ISAS .asm, TASM .asm, WLA .asm, and RGBDS .asm), and has different Game Boy Color color emulation modes. It can also import GBTD and GBMB (popular tile and map editors for Windows) files. All mouse buttons draw, and there are loads of keyboard shortcuts. It can also optionally emulate the Game Boy's display.
Tux Paint is a simple and entertaining drawing program geared towards young children. It has a simple interface, sound effects, and a cartoon character (Tux, the Linux penguin). Along with drawing brush strokes, lines and shapes, you can also enter text and place "rubber stamp" (or "sticker") images on the picture. Tux Paint is extensible, and could be useful in an educational environment (such as a grammar, elementary, or grade school). It's portable across numerous platforms, and runs well even on slower systems like the Pentium 133MHz.
"Tegel" is an add-on for Allegro for drawing and handling layered tilemaps. The package contains an editor and a playback library in C. There is support for multiple layers and rotated and/or animated tilemaps. The editor is easy to use, with unlimited undo, copy/paste, flood fill, and help included.
spriteconv stitches several individual still images into a single image with all the components side by side, arranged into a specified number of rows and columns. Such output images are typically used in 2D video games to realize the various states of animation for a particular graphical element, known as a "sprite".