To actually use this app, a tunnel service is required. You can run your own tunnel service on suitable infrastructure. See IPv6DroidServer for more details.

Notes:

1. This approach towards IPv6 has subtle implications on your privacy: for IPv6 connections, you have a fixed IP and you - as a person! - are easily identifyable by all IPv6 communication partners. Also, your mobile device suddenly has an IP on which it is reachable from the outside.
2. This app cannot be used when another VPN is active.
3. It is not required to have a rooted device.

About license:

You can opt for the convenience package, and install IPv6Droid right from here. It will download, install, guide you to the setup of your account details and update from time to time as new features or bugfixes are implemented.

But I am looking for supporters! So, I'd like to promote the approach that you set up a build environment (e.g. Android Studio), download the sources (see web site) and build it by yourself. That's it. You may use the tool, modify and even redistribute the sources under the terms of the General Public License. No obligations, but in this case you have the tools, you have the sources and you have the engagement that drives me to hope that you're going to play a more active part in bringing forward this client. E.g. by submitting detailed error reports, by submitting patches, by providing better artwork, writing better documentation, designing a better user experience, ...