Do not confuse yPen with sophisticated notebook applications like Google Notebook or the more feature-rich Zoho Notebook.
yPen, like other online clipboards, is just a quick tool for creating text notes online inside a neat and minimalistic interface.
No registration or browser add-ons required - just type (or copy-paste) the text in the available space and it stays there forever.
You can access your text notes via a unique URL. And there's no save button, everything you type is automatically saved.
yPen is different from other note-taking applications in the sense that it sports a tabbed interface and therefore several text clippings can be entered on the same webpage organized as tabs (equivalent to sections or pages in Microsoft OneNote 2007)
For developers, yPen also has an API to create or read yPen notes inside your application or widget.