Does anyone remember Frontier, a space trading game from the '90s? No, not that one, but a much lesser-known top-down game that only ran on Windows NT. It was released back in '95 and I found it a couple of years later when I was running NT 4 on my PC.
The game was incredibly addictive, but it was unfinished. The version I had was 0.5, and Altavista (this was a few years before Google) was unable to find a newer version. The gameplay owed a lot to games like Nethack. You started off in one solar system and then got to the next through a jump gate (analogous to descending to the next dungeon level). Over time, you'd upgrade your ship, with better shields and weapons, and progress further. Being a 0.5 release, there were a few things missing. The lack of sound was a shame, but the real killer was that there was no save system. You could play for an hour, then get hit by a stray nuclear warhead and have to start from the beginning. A game with so much potential, but it never went anywhere...
There's one down side: It's still Windows-only, and I don't have a Windows machine anymore. Fortunately, it runs very well in WINE. I've playing it on the Mac in the free version of CrossOver Games that was released last year.
Oh, and if anyone's interested, you can still download Frontier 0.5. It does have one advantage over the newer game; the AI didn't have any sensible friendly-fire logic, so you could easily destroy (and loot) friendly space stations by getting one of the ships defending it to fire while docked. This was easy to do: just get the pirates to chase you there and when their stray shots hit the station all of the docked ships will launch firing. This works really well for the black market outpost, which is protected by very powerful ships and is full of fun technology to steal.