Web apps like Google Docs, Basecamp, Gmail, Pandora, etc are just that: web applications that all live within your web browser. How many times have you quit Gmail only to forget about all the other browser windows you had open!? How many times has your web browser crashed and with it your open web apps!?
If you're wanting to be able to treat your web apps like local apps, check out Fluid (mac only). Fluid takes a website address and converts it to a local app, so rather than opening your browser to go to Google docs, you just click the google docs icon in your dock bar. Now your browser and Google docs are separate. It's awesome and free! Check it out peeps.