2.6.0 has been released!
Cowboy 2.6 greatly refactored the HTTP/2 code, a large part of which was moved to Cowlib and is now used by both the Cowboy server and the Gun client.
A large number of tickets were also closed which resulted in many bugs fixed and many features and options added, although some of them are still experimental.
Of note is the support for the PROXY protocol header built directly into Cowboy; the ability to use the sendfile tuple to send files while streaming a response body (for example you could build a tar file on the fly); and experimental support for range requests in the REST and static file handlers, including an automatic mode that lets you enable byte range requests to existing handlers with what's basically a one-liner.
Many options have also been added and many bugs have been fixed.
A complete list of changes can be found in the migration guide: Migrating from Cowboy 2.5 to 2.6.
You can donate to this project via BountySource. These funds are used to pay for additional servers for testing.
As usual, feedback is appreciated, and issues or questions should be sent via Github tickets. Thanks!