Five years ago (Monday the 23rd) the @W3C Social Web Working Group published the WebSub Recommendation¹
The test suites https://websub.rocks/ for Publishers, Subscribers, and Hubs are still up & running, as are the vast majority of implementations documented in the implementation report.
My site supports the publishing side of WebSub via the Superfeedr Hub² and there are many more supporting sites³.
Beyond publishing blog posts and realtime updates in social readers⁴, there are additional WebSub use-cases such as real time #IndieWeb search⁵ results, like Technorati except opt-in via WebSub subscriptions, and without any polling.
Such diverse use-cases are one of the benefits of building-block⁶ standards⁷ like WebSub.
If you create a new WebSub implementation, be sure to test it with the test suite⁸ and add your results to the WebSub Implementation Reports repo⁹.
Got questions about WebSub? Ask in https://chat.indieweb.org/dev
This is day 23 of #100DaysOfIndieWeb #100Days
← Day 22: https://tantek.com/2023/026/t1/indieweb-priorities-balance
→ Day 24: https://tantek.com/2023/027/t5/contrast-domain-chat-name