There was a big revolution in gaming that happened around 2000 that was one of the largest in gaming since the 1970s. It was led by the new edition of Dungeons & Dragons. (Back then they actually would wait many years before coming out with a new edition, so it was kind of a big deal.) The developers of the new D&D had recognized a basic problem with the 2nd edition of the game. Being a product of the ‘80s, it was overly complex, needlessly requiring players to use different types of dice at arbitrary, sometimes seemingly meaningless, times. It seemed like you were almost always having to go into the rulebooks, or some other manual, just to figure out what die to roll.
The developers of 3rd edition said, let’s stick to one die type for the majority of the game: the d20. The d20 was useful because it was very flexible. Your odds could be made simple by the sheer fact that each number was a 5% chance of success. So a player who needs to roll between 1-4 had a 20% chance. One who needed to roll between 1-5 had a 25% chance, and so on. If you couldn’t remember what die to use in a given situation, it was probably a d20.
Other dice were still used for various means, especially damage, which needed to change based on what weapon was being used. But a d20 was the default.
Then the developers did something very, very intelligent; something that a lot of corporate hacks don’t understand: They made it open source. Both D&D and the d20 system were open for other people to use in their game systems, as long as they gave them credit. This not only did not lose them profits, as many executives in other businesses believe would happen, but it actually made them more profits. People loved the system and used it in as many ways as they could. With the burgeoning internet, people talked about it and showed off games using the system, and because it gave credit to the original owners, everyone saw what they had developed, and were continuing to develop.
This was the year I went to GAMA for the first time, and everyone was talking about the system. There were entire panel discussions on it. At least half the booths were in some way showing off that d20 was the system in their new game; and D&D had the largest booth of all, boasting the creation of this system that now everyone used.
The genius of this was, rather than getting a few places to pay them some arbitrary licensing fee, they had every place giving them free advertising, which was worth a LOT more.
The d20 system began to fall out of favor around 2005. No one stopped liking it; in fact it’s still used in the Pathfinder game system, and several others. However, people started discovering that the inherent mathematics didn’t stand up to modern weapons. Using it as a shooting system is weak beyond the use of bow and arrows. It’s not a bad system, but people began innovating better methods for battles past the renaissance. And games in general began going through new innovations. But the d20 was one of the biggest in gaming history; not surprisingly brought on by the granddaddy of all innovative games, Dungeons and Dragons.