Many fine Rails Devs lean on Pow to locally "host" their apps in dev mode. Up until a few days ago, I really didn't use Pow very much. However, in a fit of boredom, I decided to see what it could do. The answer? Crash.
There appears to be a really odd issue in Pow (maybe due to its lax dev schedule) that affects us Tmux evangelists. If you initiate the install script while in a session, the install fails miserably. Just pop out, reinstall, and boom, all is well in your Rail's life.
As an aside, I really hope that 37 Signals doesn't abandon the project because there really has been little work on it as of late. Then again, maybe it is so well made it doesn't need any "real" maintance.