+1 For Roam. I'm a long-time Org Mode user, but was always waiting for something like Roam to take its place. Roam is a great example of how getting a few key features right can launch a tool into a league of its own.

Implementing the Zettelkasten is an explicit use-case for Roam, as documented here: https://roamresearch.com/#/v8/help/page/VURQiVZQR