Ineluki's Key Patch (v1.2)
This famous tool (which isn’t really a patch but a DLL replacement) allows full keyboard and mouse input as well es executing external programs from an RPG Maker event. It also provides MP3 support, which is very complicated and buggy, however.
Does only work with RM2k versions older than 1.50 and RM2k3 versions older than 1.05. This can be changed using Force Harmony.