I love Fate, but I think its just on the edge of what I would call "light", and some of the published implementations actually cross over that line for me. (naturally a matter of taste.)
Honestly, since the advent/dominance of a singular resolution mechanic, many games are fairly "light" in their core mechanics. However, the devil is in all the details added by those listy things. I think the recent editions of D&D are good good examples of this. The basic D20 mechanics aren't very heavy at all, but when you add all the different spell effects, maneuvers, conditions, etc. the system gets very heavy in play. (Even without those, the specificity of the movement rules would make D&D fairly heavy.) This is why Fate is on the line for me. The core mechanics are actually a bit more complicated than D20 and involve more decision points for players on each turn. However, by avoided all the "listiness", it plays much more lightly than D&D. (At least IME, IMO, etc. etc.)
I've never played Fate but I'ver read the Fate Core book and it gives me a vibe of being, in play, comparable in heaviness to MHRP/Cortex+ Heroic, which I've played quite a bit and wouldn't call light.
The actual Fate engine is fairly light IMO, capable of being boiled down to aspects, fate point economy, a four action resolution system, and stress/consequences. It spends most of its page count trying to illustrate its system through examples. I would say that it falls on the heavier side of rules light or lighter side of medium (YMMV). It's very much an adaptable system toolkit that can be easily modified for a far heavier game (see Mindjammer). Fate Accelerated, on the other hand, is full-on rules light. It's a mere 50 pages, and it's again mostly illustrative of its how-to-do-it-yourself principles.
The four actions, however, are meant to be fiction-first mechanics determined primarily by the GM rather than player decision points. The player describes what they are trying to do in the fiction, and then the GM may say "It sounds like you are trying to Create an Advantage with Stealth..." Over several years of running it, I don't think I have ever dealt with a player explicitly indicating, for example, that they are trying to Create an Advantage. My players are generally far more occupied with the fiction.
I am working on a rules light game, and one thing I've noticed over the years is 'rules light' means different things to different people. I am curious how everyone defines ruleslight, but also interested in what other posters see as examples of very effective rules light games.
I have also found it helpful to look at industry standards. What is rules medium? The average rules weightyness that we typically encounter when gaming? From there: What is lighter than that? What is heavier than that? Savage Worlds, for example, is generally regarded as Rules Medium. There have been different iterations of D&D whose "weight" has varied from the heavier end of rules medium to rules heavy. IMHO, a Rules Light Game System entails a series of rules of thumb patterns:
* Can the character sheet be written easily on a standard-sized index card?
* How quickly does it take to make a character? (And at extremes: For a novice? For an expert?)
* How easy is the dice resolution system and subsystems?
* How often would I need to consult the rulebooks for rules and content? (e.g., monsters, spells, character abilities, environment rules, items, etc.)
* How big is the rulebook(s)?
* What is required from the GM to run the game? How much session prep generally goes into running the game?
But a helpful point to remember:
a game can trick you into believing the system is lighter than it actually is. It's like designing rooms using white colors: white can make the walls and contours of the room appear and feel more spacious than it actually is.
Some games, such as Apocalypse World and Blades in the Dark games, may require a page or two for character sheets, but the playbooks provide players with almost all the play info that they need already baked into the character sheet. This means you can hand them the required sheet and jump into play fairly easily. So this results in a lighter feel since there is little need for players to consult the book for the relevant rules.