Well, even PINN is a bit limited in OSes for the Pi3B+ at the moment.
We are waiting for the maintainers of various distros to catch up with the changes necessary to support the new 3B+ hardware, so we just need a bit of patience.
In addition to Raspbian, Xbian, Arch and LibreElec are now compatible.
I see there is also a beta version of Retropie available now, but I haven't included it yet.
(PINN will currently show a few other OSes as being available for the Pi3B+ whereas in reality, they are still only available for the Pi3. Hopefully this will be corrected soon)
If you become aware of an OS that is now compatible with the 3B+, please do let me know so I can update PINN accordingly.