Here are some secret codes I am involved with. They are some of the best codes recently coded.
A replacement for Starling, the distributed message queue. Written on the JVM (Scala) because of the mature garbage collector. Has a constant performance profile regardless of the size of the queue.
The C library and the Ruby client as a matched pair. Much improved failure handling over the public builds, and Ketama hashing is built-in as always. Switching from ruby-memcache to memcached at Twitter effectively halved our cluster CPU load. (These changes are getting upstreamed, so you can also just wait.)
A Rails object cache layer for ActiveRecord. It can do primary key lookups and single index queries solely out of cache. Especially nice if you have replication lag.
A heap inspector for live memcached server instances. They said it couldn’t be done.
Pat Allan has been working hard on his Sphinx plugin. He’s adding the missing enterprisey features from Ultrasphinx, so that it can finish its years sleeping gently in legacy apps. (Facets, and non-invasive delta indexing.)
Apache 2.2.10 got a new fair balancing algorithm. Smooths out latencies introduced by single-threaded backends with high standard deviation, such as Mongrel/Rails.
Speaking of, I’m making sporadic progress on Mongrel 2, but don’t hold your breath. The main improvement will be Rack support.
A downside of my position at Twitter is meager open-source progress. But hey, we’re hiring (must be in SF or willing to move).
My RSI is slowly going away. The only real solution is to type less. And make sure to keep totally blasting your pecs.