Remnants of Skystone

Remnants of Skystone is a web-based MMORPG Platform Game that has been up since about 2009, set in in a Steampunk world where the ground has been covered by purple Haze hostile to the native life. Residing in this mist are creatures known as Mimics, which take on the forms of local flora and fauna. The people fled into the sky on a giant "float" known as Nidaria, and from their castle above they set their sights below, to retake the land that was once theirs. That's where you join in, as one of the three character classes: Aeronauts, equipped with jetpacks and ranged blasters; Ferrics, wall-climbing melee fighters with blades on their arms; and Crags, who use grappling lines to climb, swing and flail at enemies and break barriers.

This game shows examples of:

 * After the End: Some years ago, everyone lived on the ground. Then the Skystone exploded, leading to the spread of the toxic Haze and the spread of the Mimics.
 * All There in the Manual: The wiki, game guide, and developer's blog explain a lot about the game elements and the world of RoS.
 * Applied Phlebotinum: Ether and the Haze.
 * An Interior Designer Is You: You can decorate your home as you see fit, funds permitting, and can display trophies from your adventures.
 * Blade Below the Shoulder: The Ferrics.
 * Bribing Your Way to Victory: It's free to collect Spores from dead Mimics as a form of currency, but they're worth a fraction of value of Brass, the formal currency. The best way to get Brass is through buying it with Kreds (the virtual currency of host site Kongregate), and these are mostly bought with real money.
 * The Nidarian Guard is also a paid feature, allowing access to more stat-boosting and special missions. Averted in that unlocking a full-capacity Spectra Circuit (and filling it with highest level Etherillium Tubes) still takes a lot of playtime, efficient grinding or not.
 * Cool Airship: Nidaria is a flying city of inter-connected platforms lofted by balloons since before it was cool, surrounded by many other airships of varying size - the player gets one as a house for their characters, looking somewhat similar to Up.
 * The Corruption: The Haze, and the Mimics.
 * Cosmetic Award: Trophies are awarded for killing certain amounts of each kind of Mimic and industriousness in Item Crafting, co-op play and even other players showing appreciation for your interior design.
 * Cosmic Keystone: The Skystone, vaguely.
 * Death Is Cheap: The only penalties for dying are a message reading "You're Defeated!" and a return to the last savepoint.
 * Encyclopedia Exposita: Details about Mimics, trophies recounting a quest you've completed, bits of the society's Backstory, information on the way the world runs and the factions, and amusing little ads for restoratives and products all appear through collectable "Sprockets", lockets created by an NPC in Nidaria.
 * Evil Twin: There are three humanoid Mimics, who take after the player classes - the Ferromimic, Mimic Aeronaut and Mimicrag.
 * Excessive Steam Syndrome: Steam vents as obstacles, despite their supposedly having been untended for nearly two hundred years, often acting just to make you schlep all the way around through a particularly tricky "threading-the-needle" series of spikes and nasties.
 * Fungus Humongous: Some of the boss Mimics, especially the "Fungeye" boss in co-operative play.
 * Gameplay Story Segregation: The backstory would have you believe that since almost everything in Nidaria has to be scavenged, any processed materials are so precious, they will be recycled and re-used ad infinitum. Except once you use a found glass bottle to brew a drink and consume the liquid, the bottle is quickly cast aside.
 * Grappling Hook Pistol: The signature tool of Crags, both as a tool and a weapon.
 * Hello Insert Name Here
 * Hub Level: Nidaria. In-universe, it's the central hub of the cloud of floats everyone lives on. For the players, it's where the quest givers, shopkeepers and other game functions are located and the place to meet others for co-op play.
 * Item Crafting: You can grow your own fresh food, give it to chefs or brewmasters, smelt ores into metal, and roll that metal into bolts of material for sale (or if you're part of the Nidarian Guard, convert it into stat-boosting Etherillium Tubes).
 * It Can Think: Some of the mission briefings suggest that the Mimics aren't quite the mindless creatures they're thought to be.
 * Its Up to You: Nidaria has a standing army of Aeronauts called the "Rooks", and it's mentioned that they clear out Mimic-infested areas, install Ether tubes to dispel the Haze and bring you back to a checkpoint if you fall in the field. But the missions you're given are things they're perfectly able to do themselves, such as killing infestations of Mimics or reactivating Ether tubes (especially if you play as an Aeronaut), while the Rooks in a level just act as signposts or objectives. It becomes really glaring if you dress your character in impractical clothes, as the Rooks in tough, all-covering gear and gas masks wait for someone in a bikini top and shorts to do the dirty work.
 * King Mook
 * Knockback
 * Jet Pack: Defining characteristic of the Aeronauts. Runs on a blast of steam, but let's not question that.
 * Metroidvania
 * Money Spider: Mimics often drop Spores when they die, which are a secondary currency on Nidaria. This inverts the usual question of "Why do the spiders carry money?"; It's more like "Why do the Nidarians value the spores?", though it's still played straight if you wonder why the Mimics drop things like metal ores, fruit, firewood or bottles.
 * Organic Technology: The Mimic Aeronaut has a jetpack and blaster like his counterpart, but they aren't mechanical.
 * Platform Game
 * Planet of Hats: Both figurative and literal.
 * Player Headquarters: Every player gets a float of their own (the Nidarian economy must be in surprisingly good shape, given the circumstances), which they can alter to their own tastes.
 * Purely Aesthetic Gender: Women get more wardrobe options, but there's no other difference. You can choose facial hair and make-up for both genders, so you can play a female character with a full beard or a handlebar moustache if it pleases you.
 * Twenty Bear Asses: There are a number of these quests, some as missions, some as Item Crafting side-quests. Often you'll be out to collect Spores from dead Mimics, as these are the game's secondary currency after Brass.
 * Virtual Paper Doll: The clothing shop keeper doesn't mind if you try on everything in the store, but obviously you have to pay to keep it.
 * Wall Crawl: The Ferrics can climb walls and ceilings with their blades.
 * The Wiki Rule: Yup, there's a wiki for this.