pocketsnes and snes9x4d are for SNES.
picodrive is for Genesis/Megadrive.
gambatte, gnuboy and ohboy are GB/GBC emus.
gpsp is GBA.
unreal speccy is Spectrum.
scummvm is for playing classic point-n-click adventure games, like Monkey Island.
most of the others are either homebrew games or PC ports (doom, quake...)