The late Ivor Darreg built an instrument called the megalyra, applying principles of organ registrations to strings. In organs, the pipe sounding the fundamental for any note is often reinforced by other pipes sounding harmonics of that tone. Similarly, in his megalyra, Ivor had multiple strings creating a single composite tone. Megalyra-alt is my take on this idea. Many steel cross-bars lie across the six strings, held just above the strings by flexible mounts. The cross-bars are for fretting: press one down to get the pitch you want; strum all the strings as one, and get a single enriched tone.
A video of this instrument can be found among the demonstrations in this youtube playlist. In the audio clip, Megalyra-alt is double-tracked in a duet with itself.