Chouwa is a library that aims to ease the integration of Jinja2 into Django projects. It does this by providing equivalents of some of django's helper methods that depend on its template subsystem, as well as providing built-in globals and filters and providing a mechanism for user applications to introduce their own globals and filters.
bitstring is a Python module that helps to make the creation and analysis of binary data as simple and natural as possible. Objects can be constructed from integers (big and little endian), floats, hex, octal, binary, byte data, iterables, or files. They can be sliced, joined, reversed, packed, unpacked, inserted into, overwritten, and otherwise operated upon with simple functions or slice notation. They can also be parsed, searched, and navigated in, similar to a file or stream. Internally the data is efficiently stored as byte arrays. It is available for Python 2.6 and later (including Python 3).
Libxslt is a C library for GNOME which allows developers to work with XSLT. It is based on libxml for XML parsing, tree manipulation, and XPath support. Also included is 'xsltproc', a command line XSLT processor. The library is written in plain C, making as few assumptions as possible, and sticking closely to ANSI C/POSIX for easy embedding. It should work on Linux, Unix, and Windows. Though not designed primarily with performances in mind, libxslt seems to be a relatively fast processor. It also include full support for the EXSLT set of extension functions as well as some common extensions present in other XSLT engines.
Libxml2 is the XML C library developed for the Gnome project. The library code is portable (to Linux, Unix, Windows, embedded systems, etc.) and modular; most of the extensions can be compiled out. Libxml2 implements a number of existing standards related to markup languages, including the XML standard, Namespaces in XML, XML Base, Relax NG, RFC 2396, XPath, XPointer, HTML4, XInclude, SGML Catalogs, and XML Catalogs. In most cases, libxml tries to implement the specifications in a relatively strict way. To some extent, it provides support for the following specifications, but doesn't claim to implement them: DOM, FTP client, HTTP client, and SAX2. Support for W3C XML Schemas is in progress. It includes xmllint, a command line XML validator.
pyratemp is probably (one of) the smallest complete template-engines for Python (with less than 500 LOC). It has a very small set of special syntax in the templates. These features reduce complexity and the probability of bugs and lead to an easy-to-use and intuitive user-interface. It uses embedded Python-expressions (in a "sandbox"), is well documented, has full Unicode-support, and produces very good error-messages, which is very useful when creating new templates.
QuantLib is a cross-platform, quantitative finance C++ library for modeling, pricing, trading, and risk management in real-life. It is also wrapped as Python/Ruby/Scheme modules. Extensions for Excel, R, and Mathematica are available. Other such extensions are under consideration. QuantLib offers tools that are useful both for practical implementation and for advanced modeling. It features market conventions, yield curve models, solvers, PDEs, Monte Carlo (low-discrepancy included), exotic options, VAR, and so on.