"because it is an ordered key-value store, FoundationDB can use range reads to efficiently scan large swaths of data" https://apple.github.io/foundationdb/features.html I wonder how it compares to MUMPS databases like Intersystems Cache and FIS GtM?
Also, the obvious difference is that Caché is closed source and prohibitively expensive.
FiS is only FOSS on selected platforms (Linux x86, OpenVMS Alpha), and proprietary on all other platforms.