The following tools are used for documentation.
Markdown Guide is the main documentation language.
If you also want to add diagrams to your documentation have a look at Mermaid
Create Screenshots with Greenshot.
We use Snagit on the mac for screenshots and short videos.
We are creating technical videos for demos and training with Camtasia.
We use diagrams.net to create diagrams that are compatible with Visio and other formats.