Ok sure! I'm not sure how familiar you are with FG though, so maybe some things are not very obvious.
There's more than 250 kbytes of lua-code in the ruleset, all customized for Vaesen. For example there is an implementation for how the combat tracker handles attacks - which involves each of the different actions that players/enemies can take depending on the amount of successes. Since the implementation of the die-rolls (which includes modifiers from skills, attributes, effects, gear, conditions and custom modifiers) yield a resulting amount of successes (hopefully), that is transferred to the separate handler of attacks where you as the gm or the player can select the different actions for each of the extra successes in each attack. This is also where players or enemies can have their blocking or parrying applied to the attack. All handled together in a quite seamless and automated way. As someone who has about 5-600 hours of Fantasy Grounds ruleset development prior to Vaesen I had no real problems with implementing this - this might not be considered impressive but I also have 14 years of experience as a professional game programmer and I'm doing this in my spare time for what results in practically beer-money.
When you deal damage, and the automatic armor roll is made - the appropriate amount of damage is applied to the receiving end and the damage is applied uniquely depending on if it's a player, vaesen, animal or npc that's being hit. All of the mentioned parts are naturally networked. So when a player makes a roll, all of that is invoked on the client and distributed from there - that's how FG handles rolls but most of the logic is handled by the ruleset.
Now this is some of the more complex automation that's done in the ruleset, but if you think that setups like this in an engine like Fantasy Grounds is done in a few hours - I'm sorry to say that you are severely mistaken. And the sales on the Fantasy Grounds platform is not high enough to yield any riches that I can bathe in, and the engine and api's (CoreRPG in particular) has a lot of room for improvement.
However, fortunately for you - you can always implement the ruleset on your own in the fantasy grounds engine - if you have an appropriate FG license. And then the ruleset itself won't cost you anything. As long as you don't spread the work and it's only for your own use I think you're allowed to do that. However don't quote me on it - I don't know all the legal stuff
Hope that helps!