I'm something of a science fiction freak. It's my genre of choice whether we're talking about novels, movies, or video games. Thus, when I encountered Gate 88 I thought I was in heaven.
Gate 88 is a fairly simple top-down realtime strategy game in which the player is represented in the game - by a space ship. As you fly about you can build structures (provided you have sufficient resources) and your goal is to protect your base. You can build factories to produce more resources, research labs to develop new technologies, shipyards which (shock, amazement) produce ships, and various types of turrets to protect your base defenses. The game is designed with a very console-game sensibility in that it is ideally played with a gamepad, and playing with a keyboard will drive you absolutely insane.
In short, the game is much like an Asteroids RTS. The player can rotate or thrust backwards or forwards, and can shoot. As the player researches new technologies, new weapons are granted, the player and the player's minions gain more hit points, speed is improved, and so on. Your ships can be placed into groups, which can then be commanded to attack their target (each of three groups has its own target) or perhaps return to base. There is also a panic feature that resets your targets to your base, which causes your ships to return there and defend it.
All in all, the game is simple, polished, and well-balanced. Network play is where it really shines, but it's actually quite a bit of fun to play against the computer, which will become progressively more powerful each time you defeat an enemy base.
Gate 88 is available for Windows, MacOS X, and Linux. It uses SDL for basically everything (including sound and input) and uses OpenGL for graphics, so it should be fairly portable in general.