pspunk

website with a bunch of easy to follow guides on modding your psp. you can find their guide to installing custom firmware here and links to useful homebrew apps here.

PPSSPP

psp emulator. officially supports android, windows, linux, and mac, but also has builds for ios, switch, and other platforms.

NoPayStation

download psp games straight from the playstation server.follow the 'configuration and usage' section, following the areas that say 'PSP', to set up NPS Browser on your computer. you can also download .pkg files straight from their site under the browse section. be sure to use this plugin to get the files working on a modded psp.

Myrient

complete collection of psp games for every region in .iso format