Here is a free online game to learn mainly vocabulary. You will have to create an account and are free to use it.
It has multiple topics to choose from:
And it has multiple types of exercises on each topic.
One tip: don't forget to pick Luxembourgish language on top right corner:
Small note: under Linux-based systems it works best with Chrome/Chromium browser, in Firefox it has some glitches.
Enjoy!