MizPee (service)
There's no delicate way to describe this site, so we won't try. You use it when you are in a public place and need to find a clean toilet--something that's not so easy in most metropolitan areas. You can either check the service on your PC before you travel somewhere or use your cell phone's browser.

Stellarium (download)
This open source astronomy app displays all the celestial objects you could ever want to see, including stars, planets, nebulae, and constellations. It displays the night sky in various grids and from different points of view, and can show the movement of heavenly bodies in slow- or fast-motion.

Flightstats (service)
Want to check for delays, learn the current status of flights at airports, and track planes as they fly to their destination? This site offers an exceptional amount of detail, such as whether certain airports are de-icing aircraft.

Communications

Pownce (service)
On this social networking site you can send items to friends and receive items from them, including messages, links, files, and event notices. Pownce is also a kind of meta-networking service, since it imports all your friends from other social networking sites and e-mail programs, such as Facebook, Hotmail, and Twitter.

Pidgin (download)
Why can't instant messenger programs get along? With the open-source IM client Pidgin, they can. Within this single application, you can chat with people on all of the big instant messaging networks--including AIM, Google, ICQ, MSN Messenger, and Yahoo Messenger--plus many others you may not heard of, such as QQ and SILC.

Pbwiki (service)
Creating and maintaining a wiki is a great way for people to collaborate. With Pbwiki, you'll find it a breeze to set up a wiki of your own, for free. Whether you use it for a workgroup, for an entire business, or for a nonprofit or social group, it's ideal.

Make Me Sustainable (service)
Want to do good for the planet while connecting with like-minded others? Specify an activity at this site, and it calculates the amount of greenhouse gases the activity produces, in units of carbon dioxide. It then suggests how you can reduce your impact and shows you how much less carbon dioxide you'll generate as a result. You can also see what other people in your geographic area have done, or create sustainability discussion groups.

Gizmo (download)
Tired of paying massive phone bills? Cut them down to size with this free Skype-like software, which allows you to talk for free with other Gizmo users through your computer. You can make inexpensive calls from your PC to landlines and cell phones, too.

Dopplr (service)
If you travel a lot and want to share your travel plans with family, coworkers, and friends, try this site. You can put in your itinerary and have your friends enter theirs, and the site will create a map showing where everybody will be. If you discover that you and a friend will happen to be in the same city, for example, you can make arrangements for dinner, even if it's in the airport.

Talkshoe (service)
Here's a free way to participate in group voice chats with people who share your interests. Head to the site and click a chat to join, and you'll be able to talk using the Web-based app. You can create your own chats, as well. Talkshoe integrates directly into other social networking sites, such as Facebook, so you can converse with your friends from those sites too.