You may have come across several screenshot tools available for Linux. However, a dedicated screen annotation tool along with the ability to take screenshots? And, with cross-platform support (macOS coming)? Well, that sounds even better!
It focusses more on screen annotations than screenshots (only does full screen screenshots). Apart from the usual, there are shapes and stickers that can be moved and have colour changes. You can use the annotations live and toggle them off when needed for streaming/screencasting.
See Pensela: An Open-Source Tool Tailored for Screen Annotations - It's FOSS
Pensela is an interesting screen annotation tool available cross-platform. Let us take a closer look at it.