From the about page:
4store is a database storage and query engine that holds RDF data. It has been used by Garlik as their primary RDF platform for three years, and has proved itself to be robust and secure.
4store’s main strengths are its performance, scalability and stability. It does not provide many features over and above RDF storage and SPARQL queries, but if your are looking for a scalable, secure, fast and efficient RDF store, then 4store should be on your shortlist.
This was mentioned in a report by Bryan Thompson so I wanted to capture a link to the original site.
The latest tarball is dated 10 July 2012.