If you haven't, also check out Jane Street's Core/Async, which is an almost-complete replacement (and extension) of the standard library. (Info here: http://janestreet.github.io/.) I work for JS so I'm biased, but I think it's quite a nice set of libraries. Because it's been developed mostly internally, we've had a lot of freedom to fix bad decisions, so it hasn't built up as much cruft as might be expected. (Although it is still obviously far from perfect.)