MacVim
Vim, the text editor, for Mac OS X
..., function keys can be defined by the user, and the mouse can be used. Vim runs under Amiga DOS, MS-DOS, MS-Windows (95, 98, Me, NT, 2000, XP, Vista, 7), Atari MiNT, Macintosh, BeOS, VMS, RISC OS, OS/2 and almost all flavours of UNIX. Porting to other systems should not be very difficult. There are separate distributions for Unix, PC, Amiga and some other systems.