Set up LibreArp with Reaper

• Create a new track using Track / Insert Virtual Instrument on new track
• In the window that opens, select LibreArp and click Add

• Next, you need to add a synth that will play LibreArp’s output
  • Make sure to place the synth after LibreArp in the chain

• Write some chords and play them via LibreArp

Additional notes

• For more advanced setups, you can place LibreArp on its own track and use the routing in Reaper to send MIDI from LibreArp to other tracks with synths on them