According to its own site, PPSSPP is a free, legal and open source project that allows users to emulate PSP games on their PC, Apple and Android devices. PPSSPP is easy to use and has an active community and thorough FAQ page.
PPSSPP can be downloaded right from its site (for free), and it runs most PSP games right out of the box. PC users can scale up the textures and resolution settings to enhance their experience. PPSSPP is compatible with almost any Android phone and most controllers made for the PC.
To turn PSP games into files that PPSSPP can play, users do need to install some custom firmware onto their PSP devices. Users will have to be able to connect their PSP device to their PCs with a USB cable and follow the instructions on the PPSSPP FAQ.