novelWriter is an open source plain text editor designed for writing novels. It supports a minimal markdown-like syntax for formatting text. It is written with Python 3 (3.9+) and Qt 5 (5.15) for cross-platform support.
Python - Released: 22 Sep 2018 - 2,023
Collett is an open source rich text editor for writing novels, built on Qt 6.2+. It is currently under initial development and not ready for use.
C++ - Released: 14 Nov 2021 - 1