Today I added a trail particle system. It's a quake3 railgun sort of thing, mainly to be used when a bullet has some sort of extra effect attached, like fire, cold, etc. Definitely had to do a bit of perf tweaking on it - it doesn't do collisions, for instance.
The other day I started the AI code for teams. The AI has just been gunning for the player when it detects him, and doesn't do any target selection. I added a 'team' facet to each of the enemies and the player is on the 'player' team. An AI detecting a non-team entity will start attacking, and choosing from among non-team targets. This will be great to allow us to have some set-up battles that the player can barge into, and limited NPCs.
I also added an arcing weapon. Basically a spinning spiked projectile that is influenced by gravity - forcing the player to arc their aim somewhat to hit distant targets. The AI is not yet capable of wielding such a weapon, and may not be in the near future.