2020-04-05 UTC
# ↩️ It seems to be a web standard protocol rather than being a product. https://nordicapis.com/websub-common-cases-and-implementations/
Here are some things to look at:
https://indieweb.org/webmention.io
https://brid.gy/
https://indieweb.org/PESOS#Software
https://withknown.com/
https://ifttt.com/ ( twitter.com/_/status/1246687590381531138)