There's plenty more besides. My own static blog supports webmentions thanks to webmention.io, which is used by numerous other blogs. Brid.gy also uses it to trucker syndication and backfeed of comments from various silos.
I don’t know if one-off custom implementations count, but the blog of Xe Iaso (Christine Dodrill) speaks WebMention as well[1].
My personal static site has a custom implementation of dispatch and receipt of Webmentions using netlify functions. I’m sure there are many more folk quietly coming up with their own ways to do it as well.