Real-time collaborative editors are common tools for distributing work across space, time, and organizations. Unfortunately , mainstream editors such as Google Docs rely on central servers and raise privacy and scalability issues. Crate is a real-time decentralized collaborative editor that runs directly in web browsers thanks to WebRTC. Compared to state-of-the-art, Crate is the first real-time editor that only requires browsers in order to support collaborative editing and to transparently handle from small to large groups of users. Consequently, Crate can also be used in massive online lectures, TV shows or large conferences to allow users to share their notes. Crate's properties rely on two scientific results: (i) a replicated sequence structure with sub-linear upper bound on space complexity; this prevents the editor from running costly distributed garbage collectors , (ii) an adaptive peer sampling protocol; this prevent the editor from oversizing routing tables, hence from letting small networks pay the price of large networks. This paper describes Crate, its properties and its usage.