This is the live demo web client, the vast majority of events come from Wikipedia. Just opening up this link at any time should give you a sense of the sheer volume of events coming from Wikipedia across languages in real time. The API endpoint with today's events is here.

We recently released a comprehensive dataset of 15 million records with all citations by identifiers in Wikipedia across nearly 300 languages. The data has already been used in a number of analyses (see here and here from Matt Miller). It got picked up by Wired yesterday, with a nice story on a paper cited 2.8M times in Wikipedia. This data is being used by other organizations to drive digitization and open access efforts.