HyperScope

The HyperScope is a high-performance thought processor that enables you to navigate, view, and link to documents in sophisticated ways. It's the brainchild of Doug Engelbart, the inventor of hypertext and the mouse, and is the first step towards his larger vision for an Open Hyperdocument System.

The HyperScope is written in JavaScript using the Dojo toolkit and works in Firefox (recommended) and Internet Explorer. It uses OPML as its base file format. It is open source and available under the GPL.