LeoW
25
What specifically are you referring to for software that has a built-in webdav server?
Rclone/Roundsync can both serve files over the network using the webdav protocol. I haven't personally tried it but I will put it on my to-do list.
In theory you should be able to share your PC files from Joplin using rclone for windows serve feature.
Until I test it I can't say whether or not the Android client for Joplin can select webdav as it's synchronization choice and have it work. After Wednesday when my schedule frees up, I will try it.
I have only used http file serving to date.
I just turned my phone into a webdav server and was able to map a drive to it from Windows, so perhaps Joplin will work too. 
You would probably want to turn your PC into a webdav server, and then tell your mobile joplin to use webdav sync to the PC. I will test this after wednesday.
These options should work for those who absolutely don't want to put their files on a Cloud Server. A Cloud Server is easier and available 24/7 from all of your devices.