Popetech and Ally are present in Cabrillo's Canvas, as well as Canvas' own built in checker.

WebAim Contrast Checker (and bookmarklet)

CCA Color Contrast Analyzer

Fix Color Extension ( Will fix color of any website visited. Automatically fixes contrast. Will also change background color and size of font.)

Online Sound Meter

Access Guide

Bureau of Internet Accessibility

AXE free Chrome extension website checker

WAVE Evaluation Tool/Extension

Headings Map extension

Visualize Tab Extension

Text Spacing Extension

Extensions

Google Accessibility Support 

(Android,  Chrome, Chromebook, etc.)

An extension to test accessibility in different ways