PHP cache library, with adapters for e.g. Memcached, Redis, Couchbase, APC(u), SQL and additional capabilities (e.g. transactions, stampede protection) built on top.
Done. There's now an subfolder (e.g. http://docs.scrapbook.cash/1.0.0) for every version. There's also /master for HEAD, which is what all existing (non-versioned) urls will redirect to.
API reference (http://docs.scrapbook.cash/) should be generated for every tag, not just for master