What’s great about web apps is that you can use them anywhere and with any computer or mobile device. On the other hand, with most of those apps you’re locked in a closed ecosystem. Or worse, you may be handing over the rights to your content and your files when you agree to the terms of service. But it doesn’t have to be that way.
You can replace a number of popular web apps with solid open source alternatives. If you want to embrace your inner geek, you can even run many of them on your own web server. Or, you can use hosted versions of those apps which will only set you back a few dollars a month.