Transport Layer API as stand alone library

I am currently working on a project that will use Unity for the client side, but will run a custom server for performance and scalability reasons. I really like the feature set that Unity's Transport Layer API offers, however, since I am not using Unity on the server side, this complicates things.

Is there a stand-alone version of the Transport Layer API library out there, or a library with similar functionality that I could use in its place? Specifically, it should have the ability send both reliable and unreliable byte array messages. The ability to have multiple channels with different priorities and behaviors (such as only sending the most recent updates if the channel gets backed up) are all a major plus.

Obviously, I could create my own socket based messaging library, but it would take a considerable amount of development time to build a library with a similar feature set to the Transport Layer API, and time spent developing a library is time not spent working on other parts of the game.

 

It's all available through UnityEngine.Networking. You could remove all the HLAPI source from Networking and start from scratch with that if you're trying to get the binary size down or avoid name conflicts?