A database migrations tool written by the author of SQLAlchemy. It offers the following functionality:
* Can emit ALTER statements to a database in order to change the structure of tables and other constructs
* Provides a system whereby “migration scripts” may be constructed; each script indicates a particular series of steps that can “upgrade” a target database to a new version, and optionally a series of steps that can “downgrade” similarly, doing the same steps in reverse.
* Allows the scripts to execute in some sequential manner.