Joplin - an open source note taking and to-do application with synchronisation capabilities
I have an interest in personal information management, and as a heavy user of Emacs, it's hard for me to fairly evaluate software outside of Emacs, simply because I'm so used to everything Emacs provides. I tend to discount other programs because they lack some feature I'm used to in Emacs.
But with Joplin, the synchronization through NextCloud, good client support for Android, Linux, and MacOS, and end-to-end encryption, and the ability to instantly edit my notes in an external editor ('emacsclient'!) really make it my dream system for notes.