Do you know any application that uses webtorrent?

The Brave web browser.

https://support.brave.com/hc/en-us/articles/360035025231-Wha...

Also here, under "Who is using WebTorrent today?":

https://webtorrent.io/faq

Some games use torrents to distribute the bandwidth for updates.

Some server applications use torrents to sync large files across many servers.