Bay 12 Games has made $7M from the Steam release of Dwarf Fortress
Glad to see this, because they have worked long and hard on this game.  For the optimistic, divide ~$4m (post-tax) by team of 2 for ~20 years (they started work in 2002).  They've made some money in the meantime obviously, but seeing the final profit doesn't accurately capture the overall investment.  Just in case you were thinking of quitting your day job to become an overnight millionaire making indie games.