Spidergoat Economicsis a phrase Jeff Rients coined for something that has been around in games for ages: the idea that due to prevailing setting or personal conditions, your character must make do with gear that is not only suboptimal, but eccentrically so. This may be true for the whole game--and may determine in-game goals.
Spidergoat Economics isn't really just about gear--it's about how advancement and abilities are tied to developments in game (ie, finding "treasure" or looting dead enemies) rather than players designing and then getting to play the exact character with the exact katana they imagine in their head. It is not a player empowerment device-it is the other thing: It empowers either the GM or the dice to set up gear itself as a challenging starting condition with which the challenge-oriented player must contend. It is not escapist.
Most games do not give themselves over completely to Spidergoat Economics and are mostly a hybrid of the reliable and the Spidergoat.
In the old D&D systems where your spells are acquired randomly ("Chance to know each spell") and so you have to kill a boss monster with Mending, spells are Spidergoat. They are even more Spidergoat if they have horrible downsides or inconvenient durations, areas of effect, etc.
Originally (and in most OSR and DIY D&D games) magic items are distributed according to Spidergoat Economics. You can't just buy them, so you do what you can with your +2 Longsword of Volcanic Activity rather than just buying a +5 sword off the rack.
My D&D starting equipment list here is a very lite version of Spidergoat Economics--it's all normal equiment, but it isn't presumed that your character can just start session 1 with exactly what they want. In terms of armor and standard weapons, it ceases to be Spidergoat as soon as the players get to a big city.
On the other hand, my TMNT/Mutant Future Cannonball Run Post-Apoc Restaurant Reviewer game was 100% Spidergoat Economics as the character sheet shows.
Scrap Princess looked at my Shadowrun post from yesterday and provided one of the most divine examples of Spidergoat Economics yet--imagining a world of cyberpunk magic where nothing works the way you think it does because you're just a scrabbling schmuck between weird juggernauts.
"Hi-tech = reliable is a fucking techo-utopian scam . That gun with the target seeking bullets needs a wi-fi connection and the latest app download or it ain't doing shit. And if it gets knock around you sure ain't fixing it because it's planned obsolesces in the hyper markets of super capitalism chummer . Also see guns that you don't legally own but just pay a monthly licence fee for and it keeps trying to sell you micro-transactions."
...and gives lots of reasons the setting could and should be de-rationalized to explain how you ended up with such weird tech. Don't forget to read the comments!
Like all economic systems, Spidergoat Economics has implications that reach far beyond what you buy and how. It is related to randomness and to the rationing of options, and a game style devised around finding clever ways to play the hand you're dealt: Noisms recent post about how Shadowrunners could be victims of not just The New but The Weird New extends thoughts along the same tracks.
Spidergoat equipment systems are, ironically, very newbie-friendly as you never have to go "Here's a list of a jillion things, what do you want brand new person?" there are no trap options because everything is a trap. You don't buy stuff, you are assigned stuff and then decide who to target to get more stuff.
5e D&D as written--where you have enough to buy whatever armor you like and can get an "adventurer's pack" is not Spidergoat (thought the d100 chart of trinkets is kind a feint in that direction--and lovely, we at DIY D&D get what you were going for with that, whoever wrote it).
The assumption in 3.5 and 4e that you would just eventually buy magic items is very ungoat, cabron.
Post-scarcity futures are obviously not Spidergoat. (But post-post-scarcity is: this power armor was designed to work in a world of infinite solar energy but you crashed near a dying dwarf so you can use it for 3 rounds a day...)
Superhero character gen is mostly not Spidergoat as the challenge of making a coherent character out of collaged elements often results in PCs too silly to play in a genre where suspension-of-disbelief is already pretty high. These games need design and players need mostly to get what they want or it won't hold together as a character--though figuring out what parts of a hero pc you could goatify (personality flaws, npc support system, interparty relationships) is an interesting challenge. Maybe Wolverine spent so many points on badass he had nothing left over for Height or Working Well With Others.
Abstractness is fundamentally un-Spidergoat: the kinds of games or subsystems where you get a pool of points and spend them to create a thing of xxxx level effectiveness and you flavor it to taste (ie "You can call it whatever you want as long as it does 3d6 damage").
Apocalypse World is an interesting case: The setting elements describe a Spidergoat Economics scavenged and kit-bashed future but the system distributes these things in a way that sometimes allows for the players themselves to design them, which makes the character have to undergo Weird Scarcity, but the player gets, in practice, a gun that works like other guns. Usually. So like: the setting is pretty Spidergoat but the system is less so. The setting describes a scarcity the player does not have to tactically account for.
Spidergoat Economics is an easy way to make any sci-fi setting interesting, assuming you aren't attached to "I get to make the character I want to make with the stuff I want them to have" or abstraction or unfettered player-invention (though fettered player-invention is Spidergoat compatible: "it works but..."). Spidergoat is to setting what d100 is to plot. Like:
-Yes, you have the fastest ship in the galaxy but...your hyperdrive doesn't always work and it maybe isn't yours?
-RIFTS is solved instantly with Spidergoat Economics. Nice Glitter Boy armor there. Shame if the coolant tank got a leak... Reflex missiles huh? I think I saw one of those 3 years ago in a church full of mutant bats.
-Voyager is essentially Spidergoat Star Trek. Even the fucking crew is scavenged.