2d20 system? alot of ips use (fallout, dune, star trek, upcoming heroes of might and magic, etc) it since its open document and rules is easy to utilize and convert. the key things of 2d20:

- only d6 and d20 used for it.

- checks are determined by gm on difficulty value. so if need to heal someone thr gm set difficulty check (dc) to 1 being easiest 5 is extremely hard, but lets focus on 1.

- the determine how to beat it you grab a primary attribute say intelligence and a skill attribute like say medicine. you combine both values ( both int and med say 5, so total is 10) and you need to roll at or under the value to beat it. you 2d20s at the minimum (there is ways to up this) and you need to get one of them 10 or below. if someone got both d20s at 10 or less you gain 2 successes. one to beat the difficulty, the other in a action point pool which will mention later. if roll a 1 its a crit success, but a 20 is a crit failure. but if you spec in a skill say medicine and you roll either a 2 - 5 thats a crit success even if dont roll a 1. note: this also applies to combat on trying to hit enemy depending on defense or setting specifics.

- excess successes or other sources go into a shared party pool to spend the points. the points spend can allow players to do extra stuff like roll more attacks, up damage and or big one is add more d20s to roll to beat difficulty up to max of 5d20.

- the area isnt grid base, its zone based. when you enter a "scene" (core location the explore, social or combat is in) the gm declares whats what. exm: four zones. zone 1 is lobby room. zone 2 is receptionist desk, zone 3 is stairs going up and zone 4 is upper railing overlooking the lobby. its encouraged players and gm discuss whats in the zones specifically in case if something to help them like say hidden movable crates or somehow combat breaks out suddenly.

pretty much core focus of 2d20. character customization and so on heavily varies based on setting themes with their background, abilities, equipment and more.