We actually use rails just to manage our db. Rails migrations are so good and sane (including the rake generator tasks) that I highly recommend it...even if you are using nodejs or something else as your actual stack.
A full rails project is just a few KB. All you need to do each time is run "bundle exec rails generate migration AddNameToUsers"
And then follow the migration syntax to modify your schema. Rails will take care if the timesramping, rollbacks (in most cases),etc. You can manage your indexes, primary,etc everything here. You don't need to write any other rails code.
Check this whole directory as a part of your main source repo.
Another commenter pointed out a standalone gem for migrations. That might be OK, but I'd rather use mainline rails in this case.
Rails's migration is probably the only one that works in any project condition we've been through. No problem working with legacy DB. No problem using it in the DB where other team change unrelated table. You always know what change is in each migration.
Do you create a full rails project to handle migrations or what? How do you integrate that in with your other code?