"Repackers" utilize high-compression algorithms (often based on open-source tools like FreeArc or 7-Zip with LZMA2 settings) to compress game assets (textures, audio, video).
Tom Clancy's Splinter Cell: Conviction runs on a proprietary iteration of the LEAD Engine (an evolution of the Unreal Engine 2.5 customized by Ubisoft).
If you are looking for a solid breakdown of the Tom Clancy's Splinter Cell: Conviction