Flatpak is a solution for creating sandboxed software builds for GNU/Linux systems. You can find more information here.
KDE Software approach to Flatpak is still not ready. Nevertheless, it's being shaped up. If you're interested in helping, please send an e-mail to firstname.lastname@example.org.
The idea behind flatpak is that your applications will depend on a runtime. KDE provides a runtime with Qt and all KDE Frameworks 5 (except for the 4th tier) to make sure it's easily adaptable for any KDE Application and possibly most Qt-based applications as well.
This runtime can be added by following these instructions:
flatpak remote-add kde http://distribute.kde.org/flatpak-testing/ --no-gpg-verify flatpak install kde org.kde.Platform flatpak install kde org.kde.Sdk
Note: Do NOT use this in production, it's work in progress and it doesn't enable important safety features. It might also eat your pet or first-born.
Compile your application
Now you get to compile your favorite application. If you want to see how it's done, you can see some of the ones that have already been built. You can find it here.
To compile an applications, you should create a json file similar to the ones in the previous link. Then you'd just need to trigger the build and get it into a repository. For testing, I recommend just creating a local one (to publish an rsync will be required).
mkdir app repo flatpak-builder --ccache --require-changes --repo=repo --subject="Build of AWESOMEAPP `date`" app org.kde.AWESOMEAPP.json
This will do everything required and create a repository in ./repo. To test the application we add the repository (called remotes), we install the application and then we run it:
flatpak add-remote awesomeapp repo flatpak install org.kde.AWESOMEAPP flatpak run org.kde.AWESOMEAPP
Now you will see that some things don't work and you'll have the privilege to start fixing things!