Indieweb's webmention is great because it's so simple. You don't need a complex application to send or receive a webmention. You just have to be able to send (cURL) or receive (and log) HTTP POST to some URL endpoint. There's no way I could implement an activitypub client. But doing webmention receive with nginx path and log formats only took a few hours.
The IndieWeb has so many wonderful technologies and projects. Please, consider checking out the IndieWeb (Blog) Carnival!