For the past couple months, I've been pair-jamming with friends & colleagues on side projects. We'll often order in pizza, build a backlog of features we can ship in the next week or two, and work on it together (alternating who's coding using pomodoro timers). It's a lot of fun.
For what it's worth - I get the same feeling about my own projects, and frankly - helping someone else with their project can often unblock your own. Team work makes the dream work.
If that's something you're interested in, my contact details are in my HN profile. I do it for fun (& pizza!).