Agnostic is a light-weight, easy-to-learn, and flexible database migration tool in which migration scripts are written in pure SQL. It is agnostic towards database, programming language, and object relational mapper (ORM).

Here is an absurdly brief introduction to Agnostic:

~/myapp $ mkdir migrations

~/myapp $ agnostic -t postgres -u myuser -d mydb bootstrap
Migration table created.

~/myapp $ cat > migrations/add_cell_phone.sql
ALTER TABLE customer ADD cell_phone VARCHAR(255);
^D

~/myapp $ cat > migrations/add_nickname.sql
ALTER TABLE customer ADD nickname VARCHAR(255);
^D

~/myapp $ agnostic -t postgres -u myuser -d mydb migrate
Backing up "mydb" to "/tmp/tmpm8glpgaa".
About to run 2 migrations in "mydb":
 * Running migration add_cell_phone (1/2)
 * Running migration add_nickname (2/2)
Migrations completed successfully.
Removing backup "/tmp/tmpm8glpgaa".

For a not-quite-as-quick-but-still-pretty-quick start, please refer to the full documentation.