accessiBe - Making websites accessible to people with disabilities
KeywordTool.io - KeywordTool.io is the best FREE alternative to Google Keyword Planner and Ubersuggest. It uses Google's autocomplete feature to get over 750+ long-tail keywords for any given query.
Sim Daltonism - From the perspective of a color blind person, some colors are impossible to distinguish.
Google Trends - Explore Google trending search topics with Google Trends.
Coblis - If you are not suffering from a color vision deficiency it is very hard to imagine how it looks...
Keywords Everywhere - Free browser add-on for keyword volume, CPC & competition