It that leverages the multiple possibilities of open standards like Matrix to make a really cool to highlight web page contents and fostering discutions, all from any server you want :D
Also another project, cited in the README of matrix-highlight:
Interesting. I'll take a peek when I have a second. From a quick skim, I see one notable difference: Kontxt not only enables rich web collaboration, but it helps atomize the web to re-use key pieces in secondary contexts like a social network or in the future, to create new content.
See the Matrix blogs at https://matrix.org/blog/category/this-week-in-matrix/ to see how these projects have been progressing.
I think there is space for another paid competitor also built on Matrix!