Hi videosonix. I would just add to Colox's suggestions.
1. MIDI guitar is pretty amazing and plays well with REAPER - there is a demo I believe. This will work with chords unlike may solutions and seems to be good enough for live performance! Check this:
https://www.youtube.com/watch?v=G8D2jEhbN7Y
2. Kenny explains REAPER's native ability in this area here:
https://www.youtube.com/watch?v=G8D2jEhbN7Y
3. Not real time (I don't think?) but this will produce MIDI as well as pitch correct and harmonize.
https://products.zplane.de/vielklang
There is a cheap way of getting a lite version of this through the Computer Music archive (simply buying a current issue gets you access).
https://www.youtube.com/watch?v=f1EnR8R-0Ew
Be aware though that some users find it a little awkward to use and claim there are bugs although I have had some success with it.