MetaDirectory
- FirstSQL
- Java in-memory SQL92 DBMS with sane NULLs processing. Purports to actually strive to follow Codd's rules.
- LEAP
- An incomplete relational algebra DBMS. [Free software, GNU GPL]
- Jinx
Another relational-like Unix simple files database.
- NoSQL
NoSQL is a portable relational database management system without arbitrary limitsthat runs under, and interacts with, POSIX operating systems. It uses the Operator-Stream Paradigm.
- rdb
A very simple quasi-relational DBMS based on Unix shell commands.
- Starbase Data Tables
An ASCII quasi-relational database for POSIX.
- System R
The first implementation corrupted from the relational model, was the basis for SQL and DB2. A site preserving early history of a technology that became a critical business tool.
- Unity
Another Unix filter implementation of some relational ideas.
