Simplenote is a cloud-based application, accessible wherever the Internet is accessible. The same could be said for Google Docs, but Docs tries to be a complete Microsoft Office replacement, ending up with a powerful but complex interface. In contrast, Simplenote stays true to its name and offers a slick, minimalistic interface. It doesn't let you create spreadsheets, presentations, or any other Office-like functionality; just plain-text notes, with lots of ways to add, edit, and share them.
Using the intuitive Markdown format, Simplenote does allow for a modest amount of text formatting. This is the same easy-to-use formatting system used on Stack Overflow programming Q&A site, Tumblr and Posterous blogging platforms, and Reddit forums. You can make your text bold, italic, use headlines, and even create bulleted lists and links, all just by adding simple characters (such as **asterisks** for bold).
When you have just two or three notes to keep track of, there's no need for a filing system. But notes have a way of multiplying, and can quickly grow into a cluttered mess. Rather than use files and folders, Simplenote lets you tag notes. You can attach an unlimited number of tags to every note, but there is no hierarchy of tags--you cannot have "sub-tags" under a tag.
Much like Google Docs, Simplenote lets you collaborate on notes with other people. To share a note with someone, simply tag the note with the person's email address (this is one of the few points where the interface is less than intuitive). Simplenote then emails the person with a link to your note, letting them easily read your text and add their own input, even if they don't have a Simplenote account (unlike Google Docs, which requires all parties to have a Google account).
Collaborative editing is not exactly real-time--it takes a few seconds before you see any modifications the other person has made. Here, Google Docs definitely has the upper hand--Docs has a sophisticated real-time collaboration system which lets you see the other person's input instantly, right down to text selection.
For long-term collaboration and for editing complex documents, Google Docs is a far more powerful cloud-based solution. But that doesn't seem to be the use case Simplenote is targeting--its lightweight interface lends itself to day-to-day note-keeping, and its instant search feature makes it very easy to find any notes as fast as they come to mind. It's best used by someone who needs to keep short notes for themselves and share them with others who won't write a book in response. Think meeting agendas and grocery lists, not annual reports and wedding planning.
One of Simplenote's key strengths is its powerful API. There are dozens of unofficial Simplenote clients for a multitude of platforms, all letting you add and edit your notes. For a closer look at two Windows-based Simplenote clients, check out our reviews for fast and low-key and sticky-note application .
Simplenote's basic functionality is free of charge. There is also a premium version ($20/year) which adds the option to add notes by email, synchronize your notes as text files into a folder, and keep track of your notes as an RSS feed. Whether you go for the free or paid version, Simplenote offers a lean take on the "cloud notes" idea, and works very well.