issues.a11.rocks is a website project pointing out a11y failures of big web sites.
On their Github page, the authors share their motivation:
On the web platform, technologies and guidelines have been built so we can build a web that includes everyone. By analysing how companies still break accessibility nowadays, our motivation is to educate people on understanding and applying the Four Principles of Accessibility.
While I share that sentiment and understand the motivation, I am not the biggest fan of publicly shaming other people’s work (even if, as in this case, we talk about big companies, some even legally obliged to ensure accessibility). Nonetheless, the examples on this site are good showcase examples for just how much there is still to be done – and to illustrate how even apparently “small” omissions can seriously damage the inclusive properties of a website.
Update: On of its co-authors gave a talk at the a11y Berlin meetup in March 2018 (video on YouTube), with a thorough presentation of the four principles, using examples from this project.