Xournal++ - Create handwritten notes, sketches and journaling with a stylus. From solving a physics problem to keeping travel diaries. It can also be useful for adding annotations to PDF files.
Supports pressure-sensitive styluses and digital pens (e.g. from devices such as Wacom tablets, Huion tablets, XP Pen, etc.)
Possibilities:

Gobby is a collaborative editor that supports multiple documents in one session and multi-user chat. This means that it gives you the ability to edit files simultaneously with other users over the network.