Software

Minerva is a Comet server and client. It's sockets over HTTP, without the data loss and reordering bugs. There are demos in DemosMinerva. (live demo here)
Pyquitter makes your Python program quit when its source files change, which looks like reloading when run in a while(1) loop.
Coreweb is a set of tools for Closure Library, including a test runner with Deferred support, Python-like repr and equality, cross-tab communication, a deterministic clock for testing, functions to grab browser environment info, and an improved ExternalInterface bridge.
Securetypes implements securedict, a Python dict that uses secure hashing to stop algorithmic complexity attacks (and redux).
Desktopmagic grabs multi-monitor screenshots on Windows.
Webmagic helps you make twisted.web websites.
Protojson encodes your Python protobuf Messages to/from JSON-compatible objects.
Misc: Refbinder, Strfrag, Monoclock, git-svn mirror of Twisted.