Wireless Networking
If you own multiple PCs, you have probably thought about how great it would be if your computers could talk to each other, and do so securely.
With your computers all connected together, you could many cool things like:
Share a single Internet connection among all the computers in your home. Share a single printer between computers.
Access shared files such as photographs, MP3s, spreadsheets and documents on any computer in the house.
Play games that allow multiple users at different computers, And many other very cool things.