A crazy multitude by what I know of it. Reading references to the era, there seem to have something like a dozen different manufacturers in the field plus European imports on top of that - and a lot of very creative if not always terribly succesful to circumvent the Colt patent on some rather key characteristics of the revolver principle.

And let's not even start on the calibres. Not only was there a mind-boggling proliferation of different ones, we're also talking about the very transitional period from black powder to cordite propellant...