Somewhere upstairs I have a seven-string guitar, bought for curiosity value more than anything else and described then as a Georgian guitar (also seen it described as a Russian guitar). I just tuned the extra string down to low D.

YouTube clips here

Two alternative tunings appear on these clips:-

ADGCFAD

AEADFsharpBB

Or you can treat an eight-string guitar as a seven-course instrument like this guy.

Any advance on eight? I used to play a Portuguese Mandolin (Thuringer Waldzither) with nine, but they were set up in five courses GCGDA, the single string was the low G.

Ross