This may sound like a shameless plug... But we are currently developing a UDT library based on boost.asio, so that you can have an stream_socket API based on UDP.
Boost Asio Based UDT
At this point, the library is functional (you can async_connect/ async_accept / async_write / async_read stream of bytes between client and server), but we do not support messaging yet. You can use every major Boost.Asio toolkit features with it (e.g. futures, coroutines, and even using TLS above UDT)
The library is still pretty young and we encounter performance issues due to timer precision as discussed here.