OnLive is a streaming service that allows you to play games over networks on your computer. It also acts as a cloud service, holding your save files. Getting OnLive is as easy as registering, a download, and an installation.
Once you have OnLive, you can browse through their library. They have an extensive library of games, allowing users the options between 3 day access, 5 day access, and full access usage.
Having your friends for the weekend? Try a 3 day rental license for a game you can all enjoy together.
The OnLive service works over a functioning wireless internet connection, and allows you to play off of the OnLive servers themselves. This allows you to take advantage of the OnLive hardware, rather than relying purely on your own equipment.
Other than that, you can play just like normal (with your computer, with your friends, or on your own). The added bonus is that because OnLive works off of an internet connection based account, you can login anywhere and enjoy your games.
Easy to use, simple program
Allows computers of varying quality to play games at higher speeds and resolutions (dependent on internet connection)
Has a vast library of games to choose from, and a variety of purchase options (rental, full access, etc.)
Allows you to login anywhere
Quality of the games can vary based on the strength of your internet connection
Internet connection is required any time you want to play your OnLive games.