Booru

A booru (plural boorus, Japanese for "board") is a style of imageboard much like a chan, except you have to register and the images, SWFs, and WebMs you post stays up FOREVER. The result, of course, is inevitably large amounts of animu, gay furry fart porn, and CP. A booru can easily be distinguished by having a bunch of iddy biddy lolis holding up numbers on the front page bragging about how many images the site contains... DO NOT BE FOOLED! Behind every loli there are thousands upon thousands of obese lizard people gang-raping a fetus. And you're next. So, if you value your sanity, stay away... but, considering how you're you, that's a lost cause anyway...

Imageboard 2.0

Danbooru-style boards organize images based on tags, ratings, and scores. So instead of having a hierarchical organizing structure with a bunch of directories and sub-directories (or boards, such as /b/, /mlp/, /pol/, etc.) one finds images simply by searching for their characteristics. The types of tags are general (e.g., "animated"), artists (e.g., "shadman"), characters (e.g., "berry_punch"), and copyrights (e.g., "star_wars"). Ratings signify sexual content. And scores signifies how well the sites' users like certain content, a sort of peer review.

Software

The software used on boorus varies: mainly decent stuff, except the original version of Gelbooru. 95% of Booru.org's hostnames run this shitware. This is likely because Slayerduck is too poor to afford buying Gelbooru 0.2.x—so instead it's users are stuck with Gelbooru 0.1.x open-source-shitware.

Popular Boards

The most popular content is "relationship" stuff, cute stuff, and pornography. Relationship stuff is artful depictions of characters from a story. Permavirgins are loners with a giant boner for some sort of relationship with other characters or people; they feel this towards the characters of the TV shows and movies (see waifu and PSI) and also feel a connection to the other fags that what their animu or pastel colored ponies. Cute stuff is artful anime characters (OMG so kawaii!) and little ponies. Boorus were originally created for hentai and anime due to the magnitude of that subculture. And pornography is a strong stimulant; if it wasn't then everyone would die because there is no drive to reproduce.

Gelbooru: anime and hentai is the most popular because of autism and the fact that porn produces a very similar mental phenomenon compared to drugs not consumed with the eyes
Paheal and rule34.xxx: porn that is fictional fantasy yields great interest
Derpibooru: My Little Pony attracts many autists and furries (or just "cloppers") for the porn
e621 and FurryBooru: furry "art" is quite popular among the depraved fucks on the internets
Realbooru (and others): IRL porn–obviously–is also in high demand; however with just images, it is not as popular as rule 34 due to the limitations of real life.

Memes, politics, cats, other animals, and technology are also somewhat popular, but those things are like marijuana where pornography is like heroin.

A List of Boorus

rule #34 (rule34.paheal.net) – The Supreme King of boorus. Has rule 34-style porn of ~~EVERYTHING~~ loli is banned.
Danbooru (danbooru.donmai.us) – pretty much the same as Gelbooru, just a weeaboo overload.
Gelbooru (gelbooru.com) – pretty much the same as Danbooru, just a weeaboo overload. The mods will bitch at the users and ban them for unintentionally tagging incorrectly as their aliasing systems is broken.
Sankaku Channel (chan.sankakucomplex.com) – a more content liberal anime imageboard compared to Danbooru and Gelbooru—although racism is banned, even in jest. Also you only get to post 20 images then have to wait around 10 years to post more.
TheDoujin (thedoujin.com) – hosts doujinshi image series: mainly toddlercon, lolicon, and animal abuse because a cat is fine too.
e621 (e621.net) – furfag site that uses an edited version of Danbooru
Derpibooru (derpiboo.ru / derpibooru.org / trixiebooru.org) – Yes, even bronies have gotten their grubby little hands into this shit. They too are huge pussies as "racial, sexual or religious discrimination, use of racial or homophobic slurs, and other abusive content" is also banned (Rule #0). And by "other abusive content" they mean anything that criticizes or makes fun of the show or its fans; "abusive content" is serious business, for it hurts their fragile egos.
PoniBooru (pbooru.com) – for MLP:FiM images that are not allowed at Derpibooru.
Rainbooru ([2]) – another pony booru because we need another. Looks like ass.
The Big ImageBoard (TBIB) (tbib.org) – so big, much wow.
Lolicon-centric boorus (see also Lolicon#On imageboorus):
- Lolibooru (lolibooru.moe)
- Dead: lolibooru.org[3] & lolibooru.com - the latter used to be run by slayerduck until his server hosts disallowed the content—even though he had the message "All characters found on lolibooru are 18 years or older" throughout the website to try and fool them.[4][5] It was merged into the one below.[6]
- Registration only: AllTheFallen (allthefallen.ninja) and Lolicit (lolicit.org). See Chaosscizzors.
Hosted on booru.org:
- Rule 34 (rule34.xxx / porndot.xyz / sexyforums.xyz / njzi.xyz) – a shitty knockoff of paheal.
- Realbooru (rb.booru.org) – IRL sexual images
- Safebooru (safebooru.org) – only non-porn crap for pussies.
- FurryBooru (furry.booru.org) – 2nd largest board—there favicon is a bunny's anus

MMORPG

Boorus are similar to massively multiplayer online role-playing games. Users grind shit tons of empirical knowledge onto image pages and otherwise to gain points, level up,[7][8] and top the leaderboards. [9][10] However, constructive change is not the only change; sometimes vandals fight the system/seriously waste time by poisoning tags.[11][12]