Raindrop.io

Raindrop.io is an all-in-one bookmark manager that enables users to collect, organize, and share web content. It provides features for categorizing links into collections with tags, instant previews, and options for public or collaborative sharing. The service is available across multiple platforms, including web, desktop, and mobile.

Raindrop.io is a comprehensive bookmark manager that aligns very well with the URList concept. It allows users to collect, organize into collections (lists) and tag them (sections), and share these collections publicly or privately. It supports instant previews of various media types and offers a clean interface. While it doesn't explicitly mention 'Tufte-style side notes,' it does offer 'Highlights' for annotation, which serves a similar contextual purpose. The core functionalities of saving, organizing, and sharing URLs are strongly present.