Feats were one of my favorite additions in D&D 3e. To some degree they replaced the weapon and non-weapon proficiencies. More importantly, they gave a means of customizing characters that wasn’t class-based. Mostly; there were exceptions.
It seems many other designers liked feats, even became enamored of them if the number of feats I’ve seen published in the last twenty years (ow…) are any indication. One of the proto-Echelon designs was based heavily on feats, in fact, but I got over it when the interactions started to get too complex. I’ve taken to creating diagrams to explain the prerequisite relationships, it’s gotten some complex.
Feats or their analogs are implemented a few ways.
D&D 3.x-Based Games
D&D 3e and 3.5, Pathfinder Roleplaying Game first edition, a few others all work basically the same. Ever few levels a character gains a feat slot that can be spent on a feat. The character must meet all prerequisites of that feat. Classes can offer bonus feats that may or may not require that the character meet the prerequisites.
These prerequisites are why I mostly don’t like this model anymore. It was manageable when it meant a few feats in sequence, but some relationships have reached a level of complexity I don’t want to deal with.
I am thinking primarily of Adventurer, Conqueror, King System, and of Blood & Treasure here. Both have selectable abilities gained periodically that provide some benefit. These mostly do not have prerequisites, or only simple prerequisites in ACKS.
The feat model in 13th Age is very simple. At each level a character gains a feat. At first level a character is eligible to take ‘adventurer’ feats, at fifth level a character is also eligible to take ‘champion’ feats, and at eighth level a character is also eligible to take ‘epic’ feats.
Some feats have prerequisites, but these are mostly related to class abilities. If a feat has multiple tiers the character must take the lower tiers before taking higher tiers.
At least, if the feat has a class feature prerequisite. That case is called out explicitly, and it is not explicit that other feats don’t follow this. I’m still investigating, to satisfy my own curiosity, but it’s not important here.
Other Editions of D&D
I could dig into D&D 4e, 5e, and Pathfinder 2e, but I think I’ve found what I’m looking for.
At each odd level of each path (which I admit makes for something of an odd pattern), a character gains a feat slot of that path. That is, when gaining the first, third, fifth, and seventh levels of a basic path, a character can gain a basic feat. At first, third, and fifth levels of an expert path, a character can gain an expert feat, or upgrade a basic feat to expert and take a basic feat to backfill the now-empty slot. At first and third levels of a master path, a character can gain a master feat, or upgrade and backfill a lower-path feat. At first and third levels of a champion path, a character can gain a champion feat, or upgrade and backfill a lower-path feat.
Rows with ‘/F’ in the path column indicate that the character gains a feat at that path tier.
Feats exist at up to four tiers. A feat can exist at only a single tier (which does not need to be the basic tier), or at each tier, or somewhere in between. When a character gains a feat, the character gains all tiers of the feat up to the tier it was taken.
That is, if Axe Combat has basic, expert, and master tiers, a character who gains the feat via a basic path slot will gain only the first benefit, regardless of character level and highest path. If a character gains Axe Combat using an expert path slot, the character gains the first two benefits but not the third, and if the character gains Axe Combat using a master path slot, the character gains all three benefits of the feat. If the character initially gained Axe Combat with a basic path slot and later upgrades it to a master path slot, the character may backfill the now-empty basic path slot with another feat at the basic tier.