Complex sentence: Coral QQ, a modification of Tencent QQ, is another add-on for the software, providing free access to some of the services and blocking Tencent's advertisements.
Split into simpler sentences: Coral QQ, a modification of Tencent QQ, is another add-on. While Tencent charges for some services and displays advertisements, Coral QQ provides free access to some of the services and blocks Tencent's advertisements.