This project is from the SQLite team themselves. Their reasoning for it:

SQLite is sometimes used as the core of a client/server database system. While it works reliably well in such cases, the database backend module that it uses to store b-tree structures in its database file was not designed with this case in mind and can be improved upon in several ways. The HC-tree (hctree) project is an attempt to develop a new database backend that improves upon regular SQLite as follows…

It improves concurrency, adds support for replication & removes database size limitations.