4store was designed by Steve Harris at Garlik from 2006 onwards. The original design brief was a RDF store to hold one billion triples, an ambitious goal at that time. The final system was capable of holding 10+ billion triples, and has been a core part of the Garlik infrastructure ever since. Steve can be contacted at if you have any questions about the design.
4store was primarily developed by Steve Harris and Nick Lamb. Nick did the work on the clustering infrastructure, HTTP server and protocol. Steve mainly worked on the query engine and low-level index storage code.
4store is the logical successor to 3store, though it shares no code or design in common. For it's time, 3store was considered scalable (around 50MT was achievable on a single server in 2002).
If you would like to contribute work to 4store, please contact the developers on the mailing list for advice, or look at the TODO list.