Great note taking app and also good for creating a knowledge database. It can be synced using a paid plan, but it is also easy to sync via OneDrive or Google Drive. I really like it to work on complex projects for university.
Obsidian is by far the most valuable product I interact with on a day-to-day. I've been using it since the beginning and the evolution of the community and product is so beautiful. Obsidian is quite literately my second brain until I die.