Dave Winer pointed to Ricardo Mendez from his linkblog on July 10 with the title “Inbound and Outbound RSS”. I took a look at the Mendez post, he describes using Indiekit and plugins to both read and write posts. I think this is very similar to my minimal blogging tool MyStatusTool. In the Mendez setup, it sounds like he is also reading feeds that do not include rssCloud support.
Mendez also mentions work by Aaron Parecki on the Monacle social feed reader/writer. This tool used the Micropub and Microsub specs for publishing and subscribing. The above link is from 2016, so you can see that this predates both the MyStatusTool and rss.chat tools.