Question: I would like a lock for a garage door (roll up style). I would like the lock to be something I can control electronically, and also I would like it to retain it's state when the power is removed. 

The power requirement seems to rule out any type of electromagnetic lock, and I considered a solenoid, but I'm not sure if I can get one that stays in the current position when the power is removed. 

I think there are two types that will work - one with a latch on a solenoid (<https://www.adafruit.com/product/1512>) or possibly a small linear actuator that could be extended through a plate to lock the door. Are there any other options I'm overlooking?

Answer: 
You can get latching solenoids which fire back and forth given a current pulse. They stay in position when the current is removed.
You could consider using a motor/servo set-up. These would only use power when they're actually opening/closing the lock. For a small lock there's plenty of servo controlled units (from looking mostly for central locking on cars [like this](https://www.ebay.co.uk/i/112350866434?chn=ps&adgroupid=47842945425&rlsatarget=pla-380312364851&abcId=1129946&adtype=pla&merchantid=110247205&poi=&googleloc=1007080&device=c&campaignid=974959912&crdt=0). They need a controller to drive the servo though. 
That said, a linear actuator would also work, but would need to know when it was fully closed/opened. Whether that be by limit/reed switches or the like.