I made a tiny multiplayer RTS for XNA. You don't get direct control over your units, you only get an abstract kind of strategic choice - a balance between higher-level strategies. In a real RTS, being able to micro your units is critical, but so is knowing the higher-level strategies, and this is a toy model of those higher level strategies. In almost every RTS (with the exception of myth?), you have to maintain a constant balance between defending, attacking, and expanding - and there's an RPS relationship between them. (Turtle beats rush, rush beats expand, expand beats turtle). In this tiny RTS, instead of having direct control over your units, all you get is control over that production balance (choosing to produce more offense, defense, or econ units), and choosing how to time attacks.
Here's a screenshot of some of my attackers (the swords) on their way from my base (upper left) to the enemy base (lower right).
Design: I like the RPS relationship between the three strategies, and how your opponent's strategy is hidden from you - you have to scout out the enemy, since there's a fog of war.
I like the exponential economic growth, I think that nicely captures the quick economic ramp-up you find in RTSs. It doesn't plateau as naturally as in real RTSs, where your growth is quickly limited by various bottlenecks (like having a cap on simultaneous peon units extracting resources, or tying economic growth to expanding over the whole map).
I don't like how scouting is "free" - normally in RTSs you're sacrificing the units to do scouting. I also don't like how geography doesn't really matter - you can't position your attackers and defenders in a way that protects your base, or fighting over one resource instead of another. In an earlier version of the game, I made it so that the attackers couldn't kill econ units until all the attackers and defenders were dead, but that ended up being pretty broken.
Technical details: It's using GFWL for the matchmaking - although I hate it as a gamer, it's is super easy to code with it and XNA. However, unless you're a registered Indie/Community/AppHub developer, you're limited to playing LAN games, which is sucky. I made the game automatically host if no games are available, and automatically connect to any games that are waiting for players - so run a copy of the game on two machines on a LAN and you're set to have the most fun possible! You *may* have to create a new "offline" GFWL profile to make it not search for games on the internet :(
It's a clickonce installer, which is pretty slick (although the installer UI can be a little janky, it's cool that it automatically installs and updates itself with barely any work on my part). The source is available on the codeplex project page, but it's nothing special.
As for networking, it's a lockstep/deterministic simulation that sends user input over the network before it's used in the simulation (in the style of starcraft), so it's really low bandwidth, at the cost of a fixed 250ms latency on your input. It's been forever since I've done any networking code, and I'm glad this was relatively straightforward (with a couple desyncing bugs).
I stole the barycentric-allocation-triangle idea from simant :)