Development chat takes place on #opus on irc.freenode.net (→web interface)
The Xiph.Org wiki has an Opus TODO page, and the IETF Codec WG page has list archives, meeting minutes, and technical presentations. Monty's CELT demo page provides a broad overview of the MDCT layer of Opus.
See the documentation for an API reference and test vectors for verifying your implementation.
Opus-tools includes a set of tools for encoding/decoding Opus to and from wav. The files the tools produce are suitable for distribution with support for seeking, metadata, and multichannel. See also: the OggOpus mapping.
$ git clone git://git.xiph.org/opus-tools.git
Manpages: opusenc, opusdec, opusinfo
Opusfile provides a high-level API for decoding and seeking within .opus files similar to what libvorbisfile provides for Vorbis.
$ git clone git://git.xiph.org/opusfile.git
The Opus continuous integration server
performs automated builds and tests of Opus on many platforms and configurations.
Some of the builds run on remote systems and may fail from time to time due to connectivity problems. The console output is available and usually very informative when builds fail.