Open Source Collaboration Software
HedgeDoc
HedgeDoc, formerly known as CodiMD is an open-source collaborative markdown editor. HedgeDoc provides collaborative features that makes it easy for teams to work together by creating notes, graphs and even presentations in real-time. With HedgeDoc, all you need to get started is to share a link to your co-workers, and they can join you in the process.
OpenBoard
OpenBoard is an interactive whiteboard for schools and universities. With OpenBoard you can use a pen tablet, an interactive whiteboard or even a mouse to write and annotate your course. The software is also designed to be easy to use, yet powerful enough to facilitate most usecases, so that you can focus on your presentation rather than the software itself.