I believe they were called Express Logic. They were a real-time OS vendor based in (IIRC) San Diego. We used their OS, and (perhaps because it was stable) let our support contract lapse. Then we found a bug in the OS. We called them and asked if they could fix it, and oh by the way, our support has lapsed. They said, "Doesn't matter. We wrote it, we'll fix it." They didn't even ask us to renew our support contract first. They just fixed it, for free, for a customer that was out of support.
Microsoft bought them. I don't have any data on whether the insanely helpful support approach is still in effect.