From Wikipedia, the free encyclopedia

Obsidian is a personal knowledge base and note-taking software application that operates on Markdown files. It allows users to make internal links for notes and then to visualize the connections as a graph. It is designed to help users organize and structure their thoughts and knowledge in a flexible, non-linear way. The software is free for personal use, with commercial licenses available for pay.

This is the note app I tried before Trilium, I switched to Trilium because it has better syncing out of the box and is open source. The plug-in support for Obsidian is a better experience though. And Obsidian is better known.