- An actual language that does much database work.
- A generator for context-free-grammar parsers, written in and for PHP. (This is way cool, dudes.)
- A wikifier .
- A big load of automata theory reduced to practice.
- The latest and greatest Functional PHP Extensions, although those are growing old.
- A database abstraction layer that works with mysql and postgres. (It can easily be extended to others.)
Plenty of database "abstraction" layers are in point of fact merely shields over the fact that servers in general and PHP in particular have different C-level APIs for getting SQL commands to the server.
Instead of typing "mysql_foo" and "psql_foo", you'll instead type "db_foo" and have it work everywhere.
The ORM/QL language is smaller than SQL. It doesn't try to do everything, although it does a fair bit. You may still wind up writing some explicit SQL, but at least then you know where to focus your efforts when it comes time to port your code.