Roam Research
An outlining app that has gone through a great deal of controversy, for being far more expensive than competitors and for having a CEO who belittles his own customers.[1]
On a technical level, being web-only and with no mobile app makes it hard to use on the go. Some have complained it becomes slow over time.
Use Tana Inc or Logseq instead.
Other's opinions
Nick Milodragovich on Why Obsidian Will Overtake Roam
CGP Grey spoke about why he doesn't like Roam on a podcast