I wish it was not C++ but their implementation is quite interesting. Not only is it modern but they wrote their own standard library including error handling right down to the main function. It is quite nice for C++.
All that came from SerenityOS. I hope they do not lose too much of it with the split. I mean, the Ladybird Project Leader authored most of it ( their C++ framework ) so it will probably stick. Harder to do when you start using other libraries though.