There's the BigSQL fork, which had at least some minimal support for 10. I've no idea whether it's had / needs anything for 11
I just installed BigSQL's v11 of the database to get the pgAdmin3 that comes with it (I couldn't get the Windows installer to install just pgAdmin, I had to take the entire server installation along with it) . Even though it comes with v11, when you start it says it only supports up to v10, and then gives a series of warnings about catalogs and system admin functions not being as expected. Once you are past the warnings, it does work at least on the surface, but I have to think some features aren't going to work.