The MiSTle project is a successor of the MiST and MiSTer projects and aims to liberate the development of retro FPGA devices.
To achieve that goal the MiSTle project provides firmware source code, FPGA core source code and even open hardware designs, allowing anyone to either build and enjoy existing setups or build upon them and improve them to their own liking.
MiSTle is meant to make you independent from any software or hardware manufacturer and allows you to implement the retro FPGA device you always wanted.
For more information visit the Wiki