I would like to see a website like CapFriendly that would focus on the NBA, NFL, or MLB.
I haven't really seen anything like this for any of the other 3 sports.
The closest thing I've seen is Spotrac.com. Although I have seen errors on there from time to time, more so than on CapFriendly. And you have to pay for their premium service to see full history of a player.