Zeksa is an interesting new writing tool that combines a workflowy-like outliner with the ability to output to formatted PDF the way Scrivener or Ulysses do.

https://zeksa.com/

Discussion on Reddit:

https://www.reddit.com/r/Workflowy/comments/fcmtby/hi_i_made_a_writing_tool_inspired_by_workflowy/

I haven't really used it (lack of mobile support is a no-go for me - it actively blocks mobile Safari), but it seemed perfect for this forum.