Mule is a Python API for accessing the various file types used by the UM; the UK Met Office's Unified Model.
Along with the Mule modules itself are some utilities; these are written using Mule and provide a handful of common types of operations (printing file contents, comparing files etc.). There are also some Python extension modules which enable the usage of various libraries that provide better performance and/or identical behaviour to the UM itself. Some of these expose libraries from Shumlib (https://github.com/metomi/shumlib) and others use UM libraries (available under license only) - see the README files of the individual module folders for more information.
Note that this Git repository is provided purely as a means to allow public access to Mule, rather than as a base for development - the actual development of Mule takes place on the Met Office's Science Repository Service at https://code.metoffice.gov.uk/ (this is a restricted site with controlled access for UM partners). As a result one should not expect to see pull-requests etc. actioned directly (issues and feedback are still welcomed but will be migrated to tickets within the SRS for development).
Although the UM has a restricted commercial licence, Mule is available under the more permissive BSD 3-Clause licence. The aim of this is to allow maximum flexibility and as few barriers to usage as possible. However we would still encourage the feedback of modifications and developments (particularly bugfixes) rather than modified redistribution.
Documentation for each module is provided within a doc directory and can be built using Sphinx.