From Jos Maas:
MPL is a tool to make changes to MIDI files in batch and to process (send and receive) MIDI messages in real time. You can use it to automate your MIDI file editing work. Or build your own real time MIDI tools, like sequencers. You can load and process up to 20 MIDI files at the same time. Open multiple input and output ports. Synchronize with other sequencers. Programming is extremely easy compared with other languages.