Games for Windows Software Setup 3.5, is up for grabs free of charge.
"Games for Windows Marketplace delivers great games at great prices and gives you access to Games for Windows - LIVE, a free online gaming service that lets you connect and play with your friends and millions of Xbox LIVE members," reads the official description of the product.
Essentially, Games for Windows Marketplace Software Setup 3.5 is the replacement for the old Games for Windows LIVE client.
It's important to note that Games for Windows Marketplace isn't only an online game shop, but also a Cloud service designed to foster and support the gaming community and a distribution channel.
At the same time, Microsoft leverages Games for Windows Marketplace in order to serve game updates and patches to games, in addition to letting them find titles, buy and download them.