Govloop Academy: 

A plain language tutorial for creating plain language materials and documents within the US government or organizations

• Plain language tutorial

Readable.com:

A free tool to create "easy read" materials.  Click on the pink box "Test your readability" to access the free version.

• Readable.com

Examples of plain language documents

• Ableism and violence

• Proud and Supported: definitions and beyond

• Fighting for fairness