1.  Draw.io   (https://www.draw.io/)

• open source, no sign-in required, operate from web browser
• needs access to a desktop storage area or cloud-based - e.g., Google Drive, Dropbox, MS OneDrive or Device
• supports flowcharting, mindmapping, simple drawings
• not collaborative?

How to:

Draw.io in 82 seconds -

10 Tips for using draw.io -

2.  Google Draw

• you'll need a free Google account
• Google Draw allows you to build your drawing with others you invite
  
• you can insert hyperlinks or images to augment drawings
• your drawing can be exported in different formats
• there are settings for downloading and printing your drawing
  

Tutorials:

• Heidi Weber - (5:56)
• Will Codilla - (12:13)

3.  Microsoft Powerpoint (drawing tools)

• commonly used in workplaces and education - desktop version should be available easily
• prior to Office 365, drawing tools could be accessed from the Drawing ribbon group (Home) or under Insert menu to add shapes.
• Powerpoint 2016 has ink drawing tools too!
• SmartArt shapes not necessary but, if you know how to use them, go ahead
• free access to cloud-based Powerpoint (has drawing tools) - you'll need to sign up for a Microsoft account - https://office.live.com/start/PowerPoint.aspx 

Help docs