getmail is intended as a simple, secure, and reliable replacement for fetchmail. It retrieves email (either all messages, or only unread messages) from one or more POP3, SPDS, or IMAP4 servers (with or without SSL) for one or more email accounts, and reliably delivers into qmail-style Maildirs, mboxrd files, or through external MDAs (command deliveries) specified on a per-account basis. getmail also has excellent support for domain (multidrop) mailboxes, including delivering messages to different users or destinations based on the envelope recipient address.
Pysync has both a demonstration implementation of the rsync and related algorithms in pure Python, and a high speed librsync Python extension. The pure Python is not fast and is not optimized, however it does work and provides a simple implementation of the algorithm for reference and experimentation. It includes a combination of ideas taken from librsync, xdelta, and rsync. The librsync Python extension is less flexible and harder to understand, but is very fast.
python-jabberbot is a Jabber bot framework for Python that makes it easy to write simple Jabber bots. One can use these Jabber bots to provide information about running systems, to make Web sites interact with Jabber-enabled visitors, or notify the bot owner about updates or changes that are monitored with custom Python scripts.
Papercut is a multi-threaded NNTP server written in Python. Its main objective is to integrate existing Web-based message board software (Phorum is one of the supported ones) with a Usenet front-end. However, its extensibility enables developers to write their own containers for the storage of the Usenet articles (messages). That means that the code is extensible enough that you could write new containers to integrate the news server with other Web message board projects or even other ways to store the messages.
Hep Message Server is software that transfers messages between different messaging systems. Eventually, it should transparently route messages between email, weblogs, and instant messaging. Currently Hep does one thing: fetches news feeds from Web sites and lets you view them in your email client.
Xmpppy is a Python library grown from the jabberpy project. Though this library has borrowed some code from jabberpy, it is a separate project with its own architecture and slightly different API. It is primarily intended to be used with the RFC-compliant jabber servers (like ejabberd), but it should work with all popular servers (including GTalk).
python-fchksum is a module used to find checksums of files (or stdin). It supports md5, crc32, cksum, bsd-style sum, and sysv-style sum. The advantage of using fchksum over the Python md5 and zlib(.crc32) modules is both ease of use and speed. You only need to tell it the filename, and the work is done by C code.