xrxs
xrxs is a framework for exposing program APIs as 9p filesystems. It's written in plan9 C and intended to be coupled with uxn. 9p is an ideal API boundary to let the uxn instance focus on user-presenting behavior and business logic to be encapsulated in the backend process that exposes the 9p server.
xrxs was originally built from the top down as a monolithic game server for serving uxn cartridges and providing rudimentary networking capabilities. The new implementation is instead built from the ground up with generic features tailored to quickly creating 9p filesystems that can be used case-by-case as backend servers for applications, and uxn instances can interact with them through the File devices.
The reimplementation of taro as a xrxs application was promising, greatly reducing the complexity over the input/output streaming used previously. More experiments in this direction to come, and as those evolve the xrxs library will accumulate useful functions for building more applications.
The prototype is still available and documented and the xrxs deep dive blog post is still there if you're curious.