Emacs

Niklas Luhmann’s Zettelkasten is becoming increasingly popular for being a great note taking technique. However, it is often misunderstood as taking notes without any structure, whereas Luhmann actually structured his notes hierarchically, but also allowed for arbitrary links between notes.

Emacs can be used effectively as an email client to quickly write emails using familiar keybindings, as well as easily linking emails to org files for reminders.