Potestas has a long history going back to the very late 1990s, now 10 years ago. In short, it's my ongoing attempt to define a set of game mechanics that best describes how the important things in my game world, Selentia, are resolved. Parts of Selentia date back to the late 1980s, so this has been a long-term project! The lineage of Potestas begins with Dragon Warriors, then 3rd edition Dungeons & Dragons, then 3.5 edition Dungeons & Dragons, then a fantasy d20 rules system, and now the current system. This iteration was inspired by my exposure to 4th edition Dungeons & Dragons and my experiences playing Living Greyhawk over the past three years.
As you're probably aware from the iterations of Potestas on my website, I've been looking for many years for game mechanics that model how things in Selentia actually happen. Looking at 4th edition D&D, I was pleased to see that it tries to address several of the game features I found problematic when using 3rd edition D&D for Selentia, such as iterative attacks, too many magic items, and spells as limited resources. Unfortunately, 4th edition D&D has limited capacity to do anything other than tactical combat, which was a great disappointment to me. I didn't want a game system that said, "combat is very detailed, everything else you make up as you go": I think the game system sends strong messages to participants about what you think is important in your game, and Selentia isn't supposed to be all about the combat. My experiences in Living Greyhawk with people (players and DMs) not wanting to interact in any way except through combat reinforces in my mind how much baggage the game system creates, consciously or subconsciously.
4th edition D&D also had concepts I found interesting, like skill challenges and rituals. Skill challenges are an attempt to make non-combat conflicts more detailed and structured, and thus involve more participants in non-combat activities. Anything that moves away from the all-or-nothing non-combat resolution methods of 3rd edition seems a good idea to me - particularly when it also moves away from "one person rolls, everyone else assists" and lets each player do something their character is good at to help out. Rituals are the non-combat spells of 4th edition, but more interestingly to me, they present a model for magic that anyone with the right training can learn, because it's based off a skill check and not a class feature. I liked both these concepts, but I didn't like the ways they were implemented in 4th edition. It annoys me that combat has incremental effects, but skill challenges don't. It really annoys me that rituals are non-combat magics, and that a rogue can't get a scroll of magic missile (now a wizard class ability).
Finally, I really didn't like the way 4th edition implemented classes. I liked that 4th edition makes practically everyone in the game setting 1st level, and that all player character races were available at 1st level (even races that in 3rd edition had level adjustments, such as drow and minotaurs), and that races didn't have ability penalties. However, I really disliked that characters only have one class, and that every character of that class chooses their abilities from the same set list for that class and level. I perceive a real lack of versality in the character elements available through class abilities, which runs counter to my strong preference for customisation. The increase in total levels from 20 to 30 also seemed to me to foster number inflation: why add level/2 to almost all checks when the number of levels could be halved and you could add level instead?
So, all things considered, while I liked parts of 4th edition, I didn't like the whole. In many ways, the designers threw the baby out with the bathwater when making changes from 3rd to 4th edition. I did like some of the logic followed by the designers in approaching 4th edition, such as removing options (like sundering weapons) that bypassed the "core mechanic" of combat, namely doing hit point damage with many attacks to overcome a challenge and win the combat. Reviewing my Living Greyhawk experiences of using the Diplomacy skill to negotiate with enemies, I could see that some players and DMs seemed to view negotiating with opponents as another way of bypassing the "core mechanic" of overcoming a challenge - again, with combat being seen as the only way to overcome a challenge. It made me determined that all conflict should be resolved in Potestas using the same game mechanic, so that users could see that combat wasn't the best or only way to overcome a challenge.
Potestas provides that single mechanic for all conflicts by using a modified skill challenge structure for all narratively important conflicts. This removes the tactical mini-game within a game for combat. Character skills include Aim, Evade and Melee, so fighting with weapons uses the same skill check mechanics as negotiating, acting, and making jewellery. All skill challenges have the same mechanisms for achieving successes and resisting opponent's successes. Character defences are also skills: the three saving throws have become uses of Endure, Evade and Focus. Endure is used to resist physical attacks that hit, while Focus is used to resist mental attacks (such as Negotiate and Intimidate) that hit. The use of hit points to track incremental in-combat effects has been replaced with tracking successes and failures. All in all, I'm very pleased with how the concept reduces the discrepancy between combat and Diplomacy that exists in D&D and has thus existed in previous iterations of Potestas, and I hope it works well in play.
Taking out the tactical mini-game for combat encouraged me to take out other places where the system was overly detailed and specific. Potestas is now very abstract, placing greater importance on how events in the game are described by the participants than on how the game system specifies what's taking place. I've retained some of the design features of the previous iteration of Potestas that are suitably abstract, including wealth checks (so that players don't have be accountants). I also decided to incorporate narrative game mechanics like passions and drama points, as I've liked the effect of having similar mechanics in my supers game.
In addition to the 3.5 and 4th edition Player's Handbooks, Potestas has been influenced by numerous 3.5 edition publications from Wizards of the Coast products, Monte Cook's Arcana Unearthed, the Lace and Steel role-playing game, and Dave Morris' Dragon Warriors role-playing game. I've been inspired by some of the suggestions and discussions in various internet fora, including the Dragwars yahoo group, the rec.games.frp.dnd newsgroup, and the forums at ENworld. My gaming friends have provided feedback and imput into what they like and don't like in games, particularly my wife Bronwyn, who has more opportunity to discuss Potestas and Selentia with me than the others.