from Nexus D20 Core Rules - Ch 1: Overview: Nexus is a Universal D20 based RPG. Nexus is a system and a universal setting. Through it you can run any world or genre you want. Several different genre settings are laid out. You can have characters cross over from any genre that your GM wants to allow. This system can be used for a single game or a multiverse game. You can use it to play this setting, your own setting, or even published settings that you like but don't like their system. … There are several important differences with standard D20 that may confuse players at first. This was born out of SRD20 but it has evolved into its own system. … All dice rolls in Nexus D20 are made with a single D20. A considerable effort has been made to reduce the number of dice rolls involved in any one action. This increases the speed of play and gets you back into the story that much faster. Everything is a skill check now. There is no separate damage roll for attacks.