Well... a lot of commercial single speed bikes have a fixed/free hub. One side of the hub has a fixed cog, so if that's hooked to the chain the bike is a fixie. The other side has a freewheel, so if *that* cog is hooked into the chain, the bike is a singlespeed. So these bikes can sort of be both at once, since you can use them either way. They also come with brakes, which some fixed gear riders think is heresy. I like being able to stop, so I like brakes.