Replied to a tweet (Twitter)

Anyway I was wondering if there's a lightweight open source CMS out there that can out-of-the-box be easily configured to automatically syndicate posts differently to different APIs based on rules
— Scott Madin (@ScottMadin) August 15, 2020

e.g. I make a post to my personal site; if it's "short" (based on some threshold) the CMS puts it on a sidebar instead of the main feed, and syndicated the full text to twitter; if it's "long" it goes on the main feed, and a summary plus link is syndicated to twitter; etc.
— Scott Madin (@ScottMadin) August 15, 2020

As a user, I don't think about how an individual post will be presented on my site or in syndication, because reasonable defaults plus the integrations and optional special rules I've configured ensure everything goes where it should.
— Scott Madin (@ScottMadin) August 15, 2020

For out-of-the-box, maybe micro.blog , though it’s not opensource. Beyond that the two that come to mind are WordPress+plugins or @withknown+plugins for syndication.