Google Gears is a technology that allows one to use applications like Google Documents and Gmail while offline. If you wanted to continue writing but didn’t have an internet connection, you could do so just like in a word processor that is installed to your machine. Once saved you can move that document or any document to any folder. Once your connect to the internet again all the changes would sync with the online version of Google Docs.
This technology is actually not going to be pursued by Google any more. It is the end of Google Gears. This does not mean that Google is going to stop this functionality though. On the horizon is HTML5 which will provide similar if not better use of this technology.
The big problem with Gears is that Google has to program it to work with every operating system and every browser to keep it functioning. It did work on Mac at one point in time, but with Snow Leopard there was a change that made it so that Google Gears no longer worked. Whether this was intentional or not is not known. In Linux depending on if you could set it up, it might work but at times didn’t.
With HTML5, these processes will be built into the Chrome browser and there will be support for Internet Explorer, Firefox, and Safari. Since operating systems and browsers will all support HTML5 there is no chance that these Google applications can be turned off by developers or companies.