Accessible Versioned Terms of Service
AmbaNum, the French Ambassador for Digital Affairs, maintain the project Open Terms Archive, which tracks internet service terms of service and privacy policies by the hour.
Terms of Service and Privacy Policies are versioned (stored and archived) in the GitHub OpenTermsArchive/contrib-versions repository.
For change notifications they provide email newsletters, or you can use a GitHub RSS/Atom feed.
Definitely a great and important project.