That is really cool! There may have been others, earlier ones: just not that I knew of.

You came with the idea yourselves or you knew about other game developers doing that?

> Some of these replays represented more than half an hour of gameplay too.

Same... That was really my main motivation: sometimes needing to play for 20 minutes before the bug would show up.

> (we had a checksum of game state that we could check)

Ooooh I love that: that is plain bad---! So you not only had your deterministic engine, but a way to directly identify any discrepancy between the original state and the replayed one. I didn't think about that!

It's amazing that it let you identify bugs before they even stroke.