4 and 5 string Banjos
Five string banjo, one of the original American instruments. Once the banjo was as ubitiquous as the guitar, which eventually took over in popularity. Many players consider open G the standard tuning, gDGBD. Also common is C tuning, gCGBD, double C, gCGCD, and "sawmill", gDGCD. I play both fretted and fretless open back banjos, in the clawhammer style.
Tenor banjo was originally used as the rhythm/chording instrument for dixieland jazz,then tuned CGDA. These days, many Celtic players restring them and play in GDAE, one octave below mandolin or fiddle. The expensive, glitzy models still cost a pretty penny, among collectors and dixieland afficionados.
The plectrum banjo was traditionally tuned CGBD, like the low bass, or C tuning of a five string banjo, without the fifth string. Also a dixieland era instrument, for 5 string banjo players who wanted to play jazz, and not have that "pesky" drone string in the way. Personally, I like the drone string alot, but I play Appalachian music, wouldn't be the same without it.