Flyway is free open source software (licensed under the Apache License 2.0).

There are pro and enterprise licenses in case you have additional requirements. These licenses as I understand it are proprietary and hence non-free but the the community edition absolutely is free software.

I’ve been using the community edition in multiple projects for several years now and it works great, particularly in the context of Spring Boot applications.

It might not be just as polished and well-integrated as ActiveRecord is for Ruby on Rails but keep in mind Flyway is supposed to be framework-independent so it can’t be too tightly integrated.

That said, its integration with Spring Boot is really good. Just add it as a dependency and configuration and migrations during application startup will be taken care of automatically.