lib.reviews is an open platform to post reviews and a one- to five-star rating on basically anything. Anything with a URL, that is, and sensibly you are not allowed to review individual persons unless they act as a business. The system is actually pretty clever: every review is attached to an object, which is identified by one or more URLs. And if the URL points to a supported source — at the moment primarily Wikidata — the system will automatically pull in metadata such as a description from the data source.
I also like that the site is actually quite easy-to-use and uncluttered and built with full internationalisation in mind: the interface is available in many languages and supports non-English reviews as well. The only UI issue I have is that the language your review gets assigned to is based on the interface language you have chosen. This is not that intuitive and leads to quite a few mislabelled reviews, because the reviewer might be using lib.reviews in e.g. Portuguese but write an English review, not noticing that this review will be labelled as being in Portuguese. (It also makes writing reviews in multiple languages a hassle, as you always have to switch the interface language.)
I believe the future for Internet reviews should lie in decentralised networks, either federated (e.g. using ActivityPub) or fully peer-to-peer (e.g. built on top of Secure Scuttlebutt). But lib.reviews, by being open source and open data and being available in the here and now, can be an important first step towards that goal: by being open source, the platform itself can evolve towards enabling decentralisation. And even if it doesn’t, by being open data the reviews posted on lib.reviews can form initial content for any future platform.