Reaper

MIDI IN

1. Add plugdata to an empty track.
2. In plugdata, use one of the MIDI IN objects and route MIDI data from it (see example).
3. Play notes on this MIDI track using any usual method — keyboard, piano roll, etc.

MIDI OUT

1. Add plugdata to an empty track (a).
2. In plugdata, use one of the objects that sends out MIDI data (see examples)
3. Add another track. We'll call it RECEIVER (b). Load an instrument that you want to receive MIDI from plugdata on this track.
4. Click and drag the Route button of the plugdata track (c1) to the Route button of the RECEIVER track (c2).

FX

1. Add plugdata-fx as an effect device to an audio or MIDI track.
2. In plugdata, use [adc~] object to receive audio from your DAW (see examples).