Aurum

Provably fair: check any bet yourself

Before you bet you get the fingerprint (SHA-256) of a secret server seed. Your bets are drawn from that seed, your own client seed and a counter. When you rotate the seed it is revealed, and every past result can be recomputed and compared.

Shared games like Crash and Roulette use a hash chain published in advance: each round's result is fixed before it is played.