UberWriter is an open-source writing application, with markdown support and features for exporting files to PDF, RTF, ODT and HTML, via pandoc. The software allows the users to write in either fullscreen or the focus mode, that highlights the sentence which is currently written.
The default skin provides a white background, some horizontal lines and a dark font, but the users can choose an inverted skin, having a dark background and white font.
The latest version available is UberWriter 2.1.2, which brings fixes only.
Due to the fact that it is not available via any PPA or repository, the easiest way to install UberWriter on Ubuntu 18.10 Cosmic Cuttlefish, Ubuntu 18.04 Bionic Beaver, Ubuntu 16.04 Xenial Xerus, Linux Mint, Elementary OS and other Ubuntu derivative systems, you need to install and use flatpak and install uberwriter via Flatpak:
$ sudo apt-get install flatpak
$ sudo flatpak remote-add --if-not-exists flathub https://dl.flathub.org/repo/flathub.flatpakrepo
$ sudo flatpak install flathub de.wolfvollprecht.UberWriter
$ sudo flatpak run de.wolfvollprecht.UberWriter