Inventaire.io https://inventaire.io/welcome - Manage your physical books or other items (board games perhaps) and keep track of who has what when lending or borrowing items. ActivityPub enabled.
Thedesk.top - A bit overwhelmingly full-featured alternative UI to Mastodon/Firefish/Misskey/*key forks. Some aspects may be very confusing but for some, the workflow and customization it provides are powerful.