libtaxii is a Python library for TAXII Messages and TAXII Clients.
django-taxii-services is a Python/Django library for TAXII Servers. django-taxii-services uses libtaxii.
YETI is an example TAXII Server that can be used for prototyping and testing. YETI uses django-taxii-services and libtaxii.
java-taxii is a Java library for TAXII Messages and TAXII Clients.
There are a number of open source repositories for TAXII Related Projects. This is the central landing page for them.
