Our current software predates the accessibility compliance era but browser vendors have released some useful free extensions. We recommend looking at the following:
Various extensions for Google Chrome:
https://www.uwgb.edu/ds/resources/students/browser-extensions/chrome.asp
Zoom Functionality for Chrome:
https://chrome.google.com/webstore/detail/zoom/lajondecmobodlejlcjllhojikagldgd?hl=en
Screen contrast tool for Chrome:
https://chrome.google.com/webstore/detail/high-contrast/djcfdncoelnlbldjfhinnjlhdjlikmph?hl=en
Other useful Chrome tools:
https://luisperezonline.com/2014/10/15/ten-chrome-extensions-for-accessibility-and-universal-design-for-learning/
Useful free screen readers:
http://usabilitygeek.com/10-free-screen-reader-blind-visually-impaired-users/
We are currently building our next generation CRM and have identified accessibility as a key requirement.