Not one that you'd want to use.
While much of the protocol and networking code can be made common between a client and server, to make a useful general-purpose server requires all sorts of fiddly new code like interacting with OS authentication databases and the like.
A special-purpose SSH server (called Uppity) can now be built from the PuTTY source code. But it's not usable as a general-purpose server. Its purpose is to be a test harness.
If someone else wants to use this as a basis for writing a general-purpose SSH server, they'd be perfectly welcome to, of course. But they would have to take responsibility for all of the security hardening that hasn't been done; we don't have time for that, and we don't have motivation. The code is available if anyone else wants to try it.