Current collection of emulators and roms for PSP running custom firmware.
More to follow.
Simply copy the Nester_AoEX_R3 folder (the one containing EBOOT.PBP) to /PSP/GAME on the PSP's memory stick.
ROMs for this emulator can be found in the 'NES ROMS' folder in the 'Emu ROMs' directory. Copy whatever NES ROMs you want into the 'ROMS' folder (inside 'Nester_AoEX_R3' folder) on the memory stick. (NES ROMS are tiny, so I'd just copy all of them over either way!)
Copy the s9xTYLme (SNES) folder to /PSP/GAME on the memory stick.
Copy whatever SNES ROMs you want into the 'Roms' folder (this is in the 's9xTYLme (SNES)' folder)
Copy the 'EmuMaster V3.00 (GB, GBC, SMS, SGG)' folder into /PSP/GAME on the memory stick.
There are separate folders in this directory to place ROMs for each console (GameBoy/GameBoy Colour in 'Roms GBC', Sega Master system in 'Roms SMS', Sega Game Gear in 'Roms SGG'). Just copy the relevant ROMs into the relevant folders. You'll be able to navigate these folders to select the ROM you want to play in the emulator app on your PSP.