Most database migration tools are framework dependent, complicated, confusing to install/configure and a pain in the ass to write migrations for. In less than 5 minutes you can install Phinx, create and execute your first migration.
Phinx supports migrations written in both PHP and SQL. Use the PHP syntax to make your migrations portable between different database vendors or hand-code advanced queries. It's your choice.
Phinx has extensive documentation available at http://docs.phinx.org.
As Phinx executes from the command-line, it is painless to integrate with your deploy, build or CI tool.
Phinx is and will always remain completely free, open-source software. Developers are encouraged to fork, hack and modify Phinx. If you use Phinx commercially then please consider making a donation.
I'm currently working on a screencast for Phinx. More details soon!