Aldo's Pianito Play piano synthesizer in your PC keyboard with realtime wave and midi saving.
WinGroove Plays MIDI sounds under MS-Windows. The only required hardware is a sound card that supports WAVE output.
vanBasco's MIDI Player Great for listening to MIDI and karaoke files. It comes with rich functionality and an incredible user interface.
Digital Ear Real-Time Digital Ear Real-Time can analyze a recorded or live solo performance (wav file) (e.g. a singing human voice, or a musical instrument) and convert it to a standard MIDI file. * NEW: Now in Real-Time! *