DotSpots looks interesting:

DotSpots is an annotation platform that allows users to add text or video comments to any piece of text on the web. Dotspots searches through millions of online news articles, indexing paragraphs of text and using an algorithm to determine when certain passages appear multiple times across different sites.

Here’s a video that explains more:

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Dave Briggs

I'm an experienced senior manager in digital and ICT, looking for interim engagements to modernise technology teams to help organisations transform.