When you come up with a sweet new name for a site (or just yourself online), it sucks when you find out that it's been taken on some sites. NameCheckr searches dozens of sites at once to see if your name is free.
To use it, simply head to the source link below and enter in a username you want to check. It will then search across dozens of social networking sites, as well as website names with domains including .com, .net, .org, and .io. If the name's available, you'll see a green check. If not, you'll see a red circle with a slash through it.
This is especially helpful if you want to start a website or a company. Even if a domain name is available, you can easily get blindsided when your handle has been taken on half the social network sites you need. Of course, you can always negotiate with the person who owns it anyway, but if you can easily get a name that's available everywhere, that saves you the trouble.