Cactus Comments

Cactus Comments is a federated comment system built on the Matrix protocol. Readers log in with an account on any Matrix server they choose rather than one the site owner controls, comments can be read and posted in a browser or continued in any other Matrix client, and the source is open. It embeds on static and dynamic pages alike.

Federation inverts the usual arrangement in a way nothing else in this category does. In every other system the site owner holds the commenters' accounts and data; here a reader's identity belongs to whichever server they already use, so the same account works across every Cactus enabled site and the publisher never becomes a custodian of personal data.

Being able to continue a discussion in a general Matrix client is the natural consequence, and it makes comments something closer to a conversation than a form submission attached to a page.

The obstacle is unavoidable and worth stating plainly. It requires readers to have or create a Matrix account, and outside technically inclined audiences almost nobody does, which places this alongside Utterances as a solution for a specific readership rather than a general one. The trade is deliberate: perfect privacy for readers who already care about it, and no comments at all from readers who do not.