Pyndex is a simple and fast full-text indexer implemented in Python. Pyndex also includes an easy to use Bayesian classifier. It uses Metakit as its storage back-end. It works well for quickly adding a search feature to an application, and is also well suited to in-memory indexing and searching. It can handle phrase queries. It performs best in applications involving a few thousand documents, but its scaling is mostly limited by available memory.
Quotient is multi-protocol (SMTP, POP, IMAP, SIP, HTTP, Q2Q) server that helps with all your online conversations, be they over email, IRC, IM, mailing lists, or voice over IP. It is written in Python on the Twisted framework, and uses Xapian for search and SpamBayes for spam classification.