Source Sans 3
Source Sans Pro, Adobe's first open source typeface family, was designed by Paul D. Hunt. It is a sans serif typeface intended to work well in user interfaces.
Lexie Readable (formerly Lexia Readable) was designed with accessibility and legibility in mind, an attempt to capture the strength and clarity of Comic Sans without the comic book associations.
Features like the non-symmetrical b and d, and the handwritten forms of a and g may help dyslexic readers. You can read more about the story behind Lexie Readable in the Kernel.
PHont (pronounced Ay’-font), was developed by APH specifically for low vision readers. APHont embodies characteristics that have been shown to enhance reading speed, comprehension, and comfort for large print users.
The entire APHont Suite is available free-of-charge to qualified users for non-commercial purposes.