Quadrable: Multiversion DB – Sparse binary Merkle tree with partial-tree proofs

It's a DB. So you use it for storing data.

And merkle trees are what give "blockchains" their tamper protection: each state has a hash which includes the previous state's hash. (Although it'd be a list instead of a tree in the BC case.)

What's the use? I imagine 95% of companies that pretend to need blockchains could use something like this instead.

Something like off chain calculations or state management which then can be subtree’d out and used on chain. I think something like 1inch or Paraswap style of app were you need to do huge, in single tx terms, calculations to optimize trades across dexs and then provably import that work on chain. In reality because this is so new I doubt many people have any idea how to actually use it effectively right now but there is a lot of potential.