Usability 
A basic but highly usable note taking mobile web app. PicoNote looks like a good replacement for the discontinued Google Notebook.
The plain text notes can be public or private and are created and viewed using the piconote.com full web site, the mobile site or a Windows only PC application. The desktop version stores notes locally for offline access and synchronizes your notes with the PicoNote cloud for anywhere access and backup. There's also Twitter integration, you can create a note in Twitter by sending a Direct Message to piconote.
The required registration is instant and only requires you to pick a name and password, nothing else is needed not even an email address. Unfortunately you can only register on the full site. I'd really like to see PicoNote enable mobile registration to make it a self contained mobile app.