Folkfriends Autoharp/Autochord - 21 chords
The Autoharp is a very exotic instrument which enjoyed a small revival due to the movie about the life story of Johnny Cash. His wife, June Carter, who wrote the hit Ring of Fire, used the autoharp to help write the song.
All strings are pressed together. By pressing a bar different chords are created. Each chord has its own bar which lies just above the strings and mutes the strings not needed. This instrument has 21 chords: