Mentok is a library for storing and querying RDF data. Its main purpose at this point is to provide a bases for testing new approaches to query evaluation and not meant to be a fully functional or supported system. There's not any documentation to speak of, but there are some small example programs included that can hopefully provide a starting point for anyone wanting to dive into the code.
NOTE: Despite it's name, this project is not the Hexastore described by Weiss, et. al (VLDB08). It started as a re-implementation of the Hexastore system as described in their publication, but has no official connection with that work.