IPv6Droid is an Android client for IPv6 tunnels, in order to bring IPv6 support to Android mobile devices on networks that do not support IPv6 (specifically, all mobile networks in Germany at the time of writing).
Note! if you don't have an account at SixXS.net already, please check them first for tunnel application. The do not accepted new applications at the moment!
Caution! There is a bug in Android 4.4 and 4.4.x that breaks IPv6Droid (and several other VpnService based apps as well), see https://code.google.com/p/android/issues/detail?id=63349. If you have root access on your device, you can activate an option in settings; in this case, IPv6Droid will do crude changes to your devices IPv6 routes, that are reported to cure the problem. However, my advice is not to use IPv6Droid on Android 4.4!
On Android 5, this problem is cured.
To summarize: IPv6Droid can be used with stock devices, without root access, on Android 4.0x, 4.1x, 4.2x, 4.3x, 5.xx, and 6.xx+.
It supports the protocols TIC and AYIYA, published by SixXS.net. Account and registered tunnel from a provider compatible with this is a prerequisite for using this application. See https://www.sixxs.net/faq/account/?faq=10steps on how to get your IPv6 tunnel from SixXS.
Notes: 1) This client is not provided by SixXS, nor is there any relation between SixXS and the application developer.
2) 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.
3) This app cannot be used when another VPN is active.
4) 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. This convenience currently comes at a small cost.
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, ...