PDP2MIDI is a drum pad to MIDI trigger.
It is designed to be used with a piezo type drum pad plugged directly into your soundcard.PDP2MIDI turns the audio input into a MIDI signal usable by any drum VSTI. Five different versions are included! A two channel version, a seven channel version and an eleven channel version for MIDI out.
Have also tested using a guitar for the trigger input with very good results. You should be able to trigger with almost any audio source provided that the breaks between the peaks drop below the threshold. Does not work too well with piezo type acoustic drum triggers but I have got good results from these on a kick drum.
Note: not all hosts can work with this type of MIDI VST, as it is an audio in, MIDI out plugin. However using a VST chainer plugin like energyXT or other should make it useful in most hosts.