Google Docs is a free, Web-based word processor, spreadsheet, and presentation application offered by Google. It allows users to create and edit documents online while collaborating in real-time with other users. Google Docs combines the features of two services, Writely and Spreadsheets, which were merged into a single product on October 10, 2006. A third product for presentations, incorporating technology designed by Tonic Systems, was released on September 17, 2007.
Documents, spreadsheets, and presentations can be created within the application itself, imported through the web interface, or sent via email. They can also be saved to the user's computer in a variety of formats. By default, they are saved to the Google servers. Open documents are automatically saved to prevent data loss, and a revision history is automatically kept. Documents can be tagged and archived for organizational purposes.
Collaboration between users is also a feature of Google Docs. Documents can be shared, opened, and edited by multiple users at the same time. In the case of spreadsheets, users can be notified of changes to any specified regions via e-mail.
It is also possible to upload and share PDF files.
A version of Google Docs for the iPhone includes functionality for viewing presentations, along with an interface designed specifically for the device.
There is a limit on how much a user can store on his/her account. Each document must be under 500k plus 2MB for each embedded image. Each spreadsheet must be under 10,000 rows, 256 columns, 100,000 cells and under 40 sheets. A user can have a total of 5,000 documents and presentations, 5,000 images and 1,000 spreadsheets. The maximum number of spreadsheets that one can open at one time is 11. Only presentations under 10MB can be imported. User access to Google Docs is currently supported through Mozilla Firefox, Microsoft Internet Explorer, Safari, and Google Chrome. (Although Google Docs can also be used with Opera by turning on "mask as Firefox", it is not officially supported.)
Google Docs does not default to an encrypted  connection beyond the login screen, though text documents and spreadsheets can be optionally accessed through HTTPS by replacing "http" with "https" in the URL. Similarly, if a user enables the "always use https" option in the settings of their Gmail account, Google Docs (as well as Google Calendar) will also open with https, but only when accessed via the link within Gmail.
The privacy of sensitive documents may also be compromised by the fact that many people are increasingly logged into their Google Account – which provides access to services such as Gmail, Google Calendar, and Google Video – in a quasi-permanent fashion. While this unified login provides value, it also represents a potential threat to security (see cross-site scripting) because access to Google Docs requires no password check.
Google Docs originated from two separate products, Writely and Google Spreadsheets. Writely was an individual web-based word processor created by the software company Upstartle and launched in August 2005. Its original features included a collaborative text editing suite and access controls. Menus, keyboard shortcuts, and dialogue boxes show up in a way similar to what users may expect in a GUI-driven word processor, such as Microsoft Word or OpenOffice.org Writer.
On March 9, 2006, Google announced that it had acquired Upstartle. At the time of acquisition, Upstartle had four employees. Writely closed registration to its service until the move to Google servers was complete. In August 2006, Writely sent account invitations to everyone who had requested to be placed on a waiting list, and then became publicly available on August 23. Writely continued to maintain its own user system until September 19, 2006, when it was integrated with Google Accounts.
Meanwhile, Google developed Google Spreadsheets. This product introduced most of the abilities found today in Google Docs. Google announced Spreadsheets on June 6, 2006, and initially made it available to only a limited number of users, on a first-come, first-served basis. The limited test was later replaced with a beta version available to all Google Account holders.
In February 2007, Google Docs was made available to Google Apps users.
In June 2007, Google changed the front page to include folders instead of labels, organized in a side bar.
On September 17, 2007, Google released their presentation program product for Google Docs.