juji-io/datalevin: A simple, fast and versatile Datalog database
DuckDB: An "in-process SQL OLAP database management system"
EdgeDB: A "post-SQL" graph-relational database
TerminusDB
lakeFS: Dataset management with Git-like versioning
RocksDB: Persistent, embeddable KV store
circlebuilder/delightful-databases: A curated list of delightful databases in all shapes and sizes, and all FOSS.
Databases | Everything I know
SignalDB: Reactive local JS database
supabase/realtime: Listen to your to PostgreSQL database in realtime via websockets. Built with Elixir.
WatermelonDB: Lazy reactive database optimized for React
Materialize does some interesting stuff: Incremental Computation in the Database
Can get reactivity from the transaction log with Datomic-ish, e.g. ripley/xtdb.clj at master · tatut/ripley · GitHub
R2DBC: Reactive Streams API over relational databases
Logux includes reactive queries
Ditto includes reactive queries
Instant: Graph-based Firebase-ish
ccorcos/tuple-database
Kinto/kinto: A generic JSON document store with sharing and synchronisation capabilities.
SapphireDb - A self hosted realtime database for .NET
Realm: SQLite alternative with mobile-cloud sync
RxDB - A client side, offline-first, reactive database for JavaScript Applications (based on PouchDB)