Halo CE and The Delaginator reduce the ingame lag you see for multiplayer games online. Some of these custom maps are from Halo 2 2. There are over custom maps currently available for free compared to the small handfull of maps available for regular Halo.
Not modded maps like you see in halo PC, but brand new maps that are created specifically for Halo CE. This version of Halo, which was released by Gearbox, allows custom maps, which you can make using the HEK improved netcode, small tweaks, and more features. Free to download if you already purchased Halo PC.