Box Line Text (BLT) is a simple virtual whiteboarding tool. It is minimalistic and contains no visible UI for a clean screencasting experience.

Use it

• Click anywhere to create a text element
• Click and drag a straight line to make a line
• Click and drag a diagonal line to make a box
• Hold shift to use the mouse as an eraser
• Press Ctrl-z to undo creating elements

This tool generally assumes that you are screencasting from a laptop or desktop, so it is optimized for using a mouse to create figures and a physical keyboard to create text. It has limited touch and pen support. There are much better tools available for that type of interface.

There's no special feature for this. In most browsers, you can save the page as an HTML file. This should save your diagram and allow you to pick up where you left off. Screenshots and/or screen recordings may also be used to save your work.

The simplest way is to refresh the page (probably by pressing F5).

Native zoom in your browser is supported and should work for this purpose.