Gonâve Island offers almost nothing in the way of tourist infrastructure, and that is precisely the point. Visitors who come here do so to experience one of Haiti's most isolated communities, to see largely undeveloped coastline, and to travel in a part of the Caribbean that sees virtually no outside visitors.
The western and southern shores have reefs in reasonable condition — but diving requires bringing your own equipment. The main town of Anse-à-Galets has a market and a waterfront worth a walk. The interior of the island, while largely deforested, has hillside paths and views over the Gulf of Gonâve that reward the effort of getting to them. Moto-taxis are available in Anse-à-Galets to explore further afield.
Go with realistic expectations: no restaurants beyond basic food stalls, no guesthouses beyond bare-bones local options, no reliable electricity outside of a few hours in the evening. The people are welcoming and the landscape is striking in its austerity.