"Minecraft with rifles," is how many describe Ace of Spades, and not just because of the low-res visual motif. Or the fact it, too, is in beta. The team-based multiplayer CTF setup also allows players to build bunkers, dig tunnels and erect fortifications.
The objective in Ace of Spades is an intel briefcase, stolen from your opponents' terrain and brought back to your own. Teams of up to 16 players are supported.
There's a guide for playing the game; it contains everything you need to know about playing it. Free and PC-only, obviously. As value-added weekend timewasters go, Ace of Spades looks pretty strong. Those who download and play it, feel free to post your impressions in the comments.