xournal - Lightweight notetaking and sketching app.
gournal - Gournal is a note-taking application written for usage on Tablet-PCs (such as the Toshiba M200)
Xournal++ - Xournal++ is a handwriting notetaking software with PDF annotation support. Written in C++ with GTK3, supporting Linux (e.g. Ubuntu, Debian, Arch, SUSE), macOS and Windows 10. Supports pen input fr...
Stylus Labs Write - Write is a word processor for handwriting, designed primarily for tablets with an active stylus.
NoteLab - NoteLab brings the power of digital note taking to Linux, Windows, Mac OS X, and Solaris.
MrWriter_PDF - MrWriter fork. It has the ability to annotate PDF files and has a few other options.