If you want discos and CNN a long way from Stone Town, then this is not for you. But if you're looking for a beautiful, quiet, small place 10 minutes from the attractions, with friendly, helpful staff, Mbweni Ruins is it.

The hotel has sensitively incorporated the ruins of a mission school operated for freed slaves in the 19th century, and reproduced the botanical gardens established nearby by one of David Livingstone's travelling companions, and later British consul in Zanzibar, John Kirk. They have also touchingly researched and displayed the history of the mission to freed slaves.
http://www.mbweni.com/mbweniruins.htm

Take the dhow trip to view Stone Town from the sea at sunset - they sail most of the way there - book well in advance.