I've been using Webmention for almost 2 years now, and I am fortunate to use Aaron Gustafson's jekyll-webmention_io plugin for Jekyll, the static site generator I currently use on this site. Aaron's plugin deals with getting the Webmentions from webmention.io, as the name implies, but also with sending mentions to external contents I link to in my own content.
Unfortunately, most other Webmention implementations only deal with receiving, not sending, so Remy Sharp thought it would be a good idea providing such tool: webmention.app
Adding Webmentions to a site seemed straightforward and a well trodden path. Sending outgoing webmentions on the other hand seems to have been generally left to ones own devices.
So I decided to take up the challenge and build a platform agnostic method of sending outgoing webmentions, that anyone can use.
Remy supports several ways to use the tool, even available as a self hosted script.
I will not use it on my current Jekyll powered site, but I will definitely keep it in mind for the probable future migration to Eleventy.