It's called an ngoni - they are the Ngoni Band. It is a predecessor of the banjo. There was a very good article in fRoots magazine a couple of years back on Bassekou Kouyate (who has since got a lot of deserved recognition) called - wait for it - Only Ngoni.

Their album is extremely good, not a bum track on it.

Bassekou has worked as a sidesman for several years, and was originally proposed as a member of the musical project that became The Buena Vista Social Club. He has also recorded with Taj Mahal on the album he cut with Toumani Diabate (I forget the title, but it's apparently on Barrack Obama's favourite album list).