Quadrable is an authenticated multi-version database. It is implemented as a sparse binary merkle tree with compact partial-tree proofs. There are C++ and Solidity libraries, as well as a git-like command-line tool.
Ephemerand: A globally-consistent randomness beacon that extracts unpredictable data from from the GPS almanac.
Defido2: Contract-based ethereum wallet that repurposes commonly available FIDO2 two-factor login devices for cryptocurrency operations.