The underlying book and author data for many of these is sourced via a lower layer of openlibrary.org and wikidata (which in turn are building on isbns and the collective records of many national libraries) and when they aren't, they should be. The underlying data should be a shared endeavour.

Openlibrary.org provides book tracking (want to read, currently reading, have read) itself, as long as you can cope with it being neither beautiful nor social, which seem to be the key selling points of many of these.