It’s not really a full fledged web app, but I launched a WebDAV server this year:

https://hub.docker.com/r/sciactive/nephele

I use it for all sorts of things. It’s got some great features that other WebDAV servers are lacking:

• S3 support, so you can use a cloud service as the backend.
• Encryption at rest, so you can keep your data private, even when it’s stored on S3.
• File deduplication, so you can throw the same files in over and over and not use up more disk space.
• PAM authentication, so you can let system users manage their own files.
• .htpasswd authentication, so it works with other web servers.
• A simple web interface, so you can manage files in your browser (and it should work on all browsers, even absolutely ancient ones).

It’s incredibly fast compared to most other WebDAV servers, too.

I use it to manage my Jellyfin libraries, as a personal cloud storage, and as a deduplicating backup server. It works well through a reverse proxy too, so I have multiple instances running on my server with different configs.

There’s also a desktop app that uses the same server under the hood to let you transfer and manage files across your network:

https://sciactive.com/quickdav/