Metakit is an efficient database library with a small footprint. It's a cross between flat-file, RDBMS, and OODBMS.
Keywords: structured storage, transacted, load on-demand, portable, C++, Python, Tcl, instant schema versioning.
CAVOR is an engine for building apps that involve both graphic and text/numeric data. Primarily GIS is the initial focus, but consider also CAD, CASE, project management (eg PERT charts), and others. Built-in scripting, C API, also supports Tcl and Java.
Auth0 Token Vault handles secure token storage, exchange, and refresh for external providers so you don't have to build it yourself.
Rolling your own OAuth token storage can be a security liability. Token Vault securely stores access and refresh tokens from federated providers and handles exchange and renewal automatically. Connected accounts, refresh exchange, and privileged worker flows included.
PostgresSQL Replicator is an open-source asynchronous (store&forward) replica engine that provides some data ownership models and many conflict resolution algorithms.