Wayland

As of Fedora 27, Fedora ships with Wayland as the default display server. According to users' reports, there are additional manual steps required to make some applications run correctly on Wayland. It appears that this has nothing to do with AppImage specifically. Thanks @sudo-give-me-coffee for writing down the steps to do in order to make applications, e.g., Mudlet, work on Fedora:

xdg-user-dirs-update
sudo su
cd ~
xdg-user-dirs-update

If you are getting Could not connect to display :0 then you need to install XWayland

References:

• https://fedoraproject.org/wiki/How_to_debug_Wayland_problems
• https://docs.fedoraproject.org/f27/system-administrators-guide/Wayland.html