Call of Cthulhu

Basic role Playing system
Call of Cthulhu uses the Basic Role Playing system instead of the D&D d20 system. The main mechanical differences are:


 * Like real life, there are no classes. Characters can be and do whatever the player wants. If you want your character to be a baker who shoots rabbits at the weekend and likes listening to symphonies, go for it.
 * Like real life, there are no levels. As the characters do things they get a little more skilled each time. But they don’t suddenly collect enough experience that makes them twice as good at hitting things and twice as good at surviving things.
 * Like real life, your “hit points” don’t increase over time. You’re pretty much always going to be the same toughness all your life.
 * Life real life, combat hurts. If you get hit there’s a very real chance you will be seriously debilitated or die.
 * There are no “feats” - everything is decided by skills.
 * All skills are based on a percentage system. If you have 42% in shooting a pistol you roll two d10 percentage dice and if you roll 42 or lower you succeed. Roll over 42 and you fail. Modifiers to the percentage can be given for range or other difficulty.
 * “Game balance” is always difficult to estimate, but generally if you’re playing a BRP game you better learn to think before you get yourself into a fight. And if you do get in a fight, better think tactically instead of just running headlong at the enemy.
 * Combat effin’ hurts! One or two solid hits by even a modest gun, and you’re out! Even then, people get suspicious when you get into a hospital with a gun wound or a stab wound, and the police are likely to show up and awkward questions. So you really really really don’t want a fight.
 * The game is set on Earth, mostly around 1920s, but there are options for 1890s or modern era as well. So you can’t go murderhoboing like you would in a D&D game without having the police eventually chase you.

Ref: https://www.quora.com/How-does-Call-of-Cthulhu-work-and-how-is-it-different-from-standard-D-D-on-a-game-mechanics-and-game-balance-level

Roll20 Tutorial
Call of Cthulhu Walk Through with LaughLoveLindy - YouTube https://www.youtube.com/watch?v=N7uKxtoH-MY