What do you use for database migrations

I'm kind of looking for a RMDB migration tool. Ideally one that:

• Isn't tied to an application framework (e.g. it can use some programming language for its operation, but shouldn't push me to use that language for the rest of my own application).
• Works for many SQL dialects.
• Free (gratis) & open source.
• Easy to install and run (preferably not rocket science to write).

And nice to have:

• Backward migrations are nice, but not required.
• Ideally can be put in VCS to match data and code versions. So e.g. no consecutive numbering, as that gets messed up when there are many concurrent feature branches.
• Nice if it supports schema and data migrations.
• Squashing migrations would be nice.
• Plugins

No need to generate access code (ORM stuff), those can be based on the resulting schema.

So my question is: what do you use?