I am very interested in any project that implements multi-active SQLite clusters with no cluster size limit, do you have any links for me?
But if you're looking for some monolith project to provide all of this for you you're going to be in that territory of that fake open source. Because again to build all of this into one tool that has everything from the data access layer all the way down to the metal underneath to ensure that it's replicated and highly available is not a trivial task. Especially if you want things like acid compliance arbitrary joins between data structures and so forth.
The file system is effectively a database of things with an API that accesses those things. Simply a file system of properly named files and directories could meet your needs depending on what those are.
It's the complexity of your access model and methods that will determine what fits your bill.
Not sure why "no cluster size limit" is important given the goals you listed in your comment btw. The rqlite faq mentions a practical cluster size limit of 9 read-write nodes (higher for read-only replicas).
That said, very large datasets (> 2GB) will work, if you've got the disks and memory to handle it. The link above explains how to do it.
Noting the title of this topic, rqlite is specifically designed to be easy to use. I know of no other HA database that is simpler to operate. Installation is trivial, and clustering is easy. You interact with it via a HTTP API.
And you get all the power and quality of SQLite as the database engine.
But larger clusters mean a larger quorum, so larger isn't really better. It depends on what you want. If you want a distributed database where more nodes means more write performance, then rqlite may not be a good fit. rqlite is distributed for fault-tolerance and HA, not for performance.