You asked about a "cordless" nail gun. The only thing that comes to mind is the Paslode-type guns that use an explosive charge of gas. There are now other brands. They are typically more expensive that the type using a comprsssor, and you have to factor in the cost of the gas cylnders.
I used one on a job a while back (borrowed) and I was not impressed. It was a bit bulky - they all are - but the trigger action was slow and sort of funky. I guess you would get used to it after a while but I much prefer my old Hitachi pneumatic. The air hose can get in the way if you are working in close quarters, but you can handle that.