Trilium Notes is a hierarchical note taking application with focus on building large personal knowledge bases.
qpdftools
Qpdf Tools is an easy-to-use Qt interface for Ghostscript and Stapler, which makes it possible for normal users to manage their PDFs.
gImageReader
gImageReader is a simple Gtk/Qt front-end to tesseract-ocr.
Xournal ++
Xournal++ is a hand note taking software written in C++ with the target of flexibility, functionality and speed.
Produktiviti Super
Put a task into your project for today or schedule it to another day to keep your head free.
Notorious
Keyboard centric notes.
CoolReader
Cross platform open source e-book reader.
Featherpad
FeatherPad is a lightweight Qt plain-text editor for Linux.
Liri text
Liri Text is a cross-platform text editor made in accordance with Material Design.
Lifeograph
Lifeograph is an off-line and private journal and note taking application for Linux desktops and Android.
It offers a rich feature set presented in a clean and simple user interface.