Notion
Discord
These tools are still not entirely mainstream compared to tools like Notion, which is related to your experience trying to learn more about the tools - so they tend to have a steep learning curve!
IMO the best way to get a feel for what they are is to see some examples/videos.
I like this video for an overview of Logseq: https://www.youtube.com/watch?v=ZtRozP8hfEY&t=6s
I describe Roam and the Roam Discourse Graph extension in this portion of a talk I recently gave: https://youtu.be/jH-QF7rVSeo?t=1417