As we disclaim on the page itself, we aren't experts on all of these databases, so it's possible that we've made a mistake. We are relying on the documentation

As we disclaim on the page itself, we aren't experts on all of these databases, so it's possible that we've made a mistake. We are relying on the documentation of other products (but on the specific documented claims rather than whether they throw around the term "ACID"). 'Snapshot isolation' is a level of isolation guarantee, not an implementation technique. It means that a transaction will read values consistently at one point in history and then write values at a later point, even though the read values may change in between. To give a classic example, pure snapshot isolation doesn't allow you to soundly transfer $100 from Alice's account to Bob's account. FoundationDB uses MVCC and optimistic concurrency, but provides serializable isolation. Besides this, and the asynchronous indexing that you mention, RavenDB uses an "XA" type technique for cross-node transactions which relies on the durability of an external transaction coordinator. Various public statements of the developers lead me to think that they don't find this arrangement more trustworthy than I do. "Local" transactions on a single document don't qualify as ACID transactions; that's one of the primary messages of the page you are linking to.