The Cleveland Browns have a perfect testing ground for unsigned free agents, and it is the reincarnated XFL, the new league dreamed up by Vince McMahon which started play on February 8-9. There are likely to be a few NFL-caliber players who have been missed by the NFL scouting systems, and perhaps Browns scouts find a few of them.
There is nowhere near the talent level in the XFL compared to the NFL draft. But on the other hand, there is no draft for signing XFL players. No one automatically gets the opportunity to sign the best players.