[This will be part of a series of posts about conlanging and its interaction with academic linguistics.]
So, what is conlangery? It's not a popularly known art, so here's a primer for y'all who haven't ever heard of it.
The word conlang is short for "constructed language". Well-known conlangers include Ludwig Zamenhof (Esperanto), Marc Okrand (Klingon), and the revered JRR Tolkien (who once wrote that he invented Middle-Earth largely in order to give his beloved Elvish languages a place to live). We invent languages: spoken languages, signed languages, artificial siblings and alternative scripts for natural languages, artistic languages, logical languages, international auxiliary languages, mind-extending languages, you name it.
(I should warn you that conlangers, being naturally fond of playing with words, habitually `overgeneralize' and apply all kinds of grammatical forms to the word `conlang'. Just for starters, it's both a noun and a verb. A conlanger is someone who conlangs, what they create is a conlang, and the art in general is conlanging or conlangery. On top of that, the con- prefix has become productive, meaning it can apply to all kinds of invented/imagined things: conlangs, conworlds, conscripts (meaning writing systems, not military draftees), conreligions, consolarsystems, conbiology...the list goes on.)
The earliest known conlanger is Hildegard von Bingen, a 12th century German abbess. She's best known for her gorgeous music, but she also invented a language called Lingua Ignota ("unknown language"), which supposedly came to her by divine inspiration.
The best known conlanger...well, it depends who you talk to, but most people will name either Zamenhof or Tolkien, and here we come to a major split in the world of conlangery: that between auxlangers and everybody else. Auxlang is short for "international auxiliary language", and not to make any sweeping generalizations here, but the sort of people who make auxlangs are also the sort of people who have fiery and/or highly unconventional political agendas, and a lot of them are also shamelessly self-promoting. Unfortunately, if you're auxlanging in earnest, this isn't really fixable. You have to want the entire world unified, in some sense, by your language. And you have to think your language is not only `good' enough for everyone in the world to speak, it's `better' than the dozens and dozens of old failed auxlangs. A certain amount of crankery is inherent to the practice of serious auxlanging.
(Quite apart from the above, the vast majority of linguists and conlangers have a horrible visceral reaction to the thought of losing most -- if not all -- of the world's linguistic diversity. Who wants to replace all that culture, knowledge, and sheer beauty with something necessarily bland?)
(Yeah, and, in case you couldn't tell, I'm totally biased, and I freely admit it. Auxlangs are not all bad; any conlangery effort bears some useful fruit.)
So what about the `rest' of the conlangers? People conlang for all sorts of reasons, but the one that really unites us is, trite as it sounds, is love: love of language, its beauties, its intricacies, its elegances; and love of playing around with that in systems of our own creation.
This is not to say that there aren't divisions within the body of non-auxlangers. Probably the biggest group is the artlangers, like Tolkien, who conlang for aesthetics and elegance. (This is not to say that all artlangs end up looking like Tolkien's Elvish languages, all full of L and R and vowels everywhere with nary a `guttural' consonant. Conlangers have as much variation in taste as the general population. Plus, for example, there's a lot to be said for a language in which you can swear effectively. Imagine trying to shit-talk someone in Quenya or Sindarin.) At the very least, many hundreds of artlangs have been made, or at least started. My own language Tlharithad is a young artlang, though I sadly haven't had time to work on it since the beginning of the semester. You can find quite a few well-developed artlangs, associated with the fantastic conworld of Verduria, at Virtual Verduria, made by Zompist. I have to apologize to the many, many, very worthy artlangers that I haven't linked to, but for non-conlangers, Zompist's work makes a good place to start.
On the flip side of the same coin, you have the engelangers -- engelang is short for "engineered language" -- who design their languages to achieve a particular goal. There are logical languages, like Lojban, which are designed to eliminate ambiguity. And there are other engelangs, whose design goals don't really fall naturally into groups. A seminal example is Ithkuil, which has about five times the information content per syllable of natural languages. In the words of its creator, John Quijada, Ithkuil is "systematically designed to blend a high degree of communication of cognitive intent and meaning with a high degree of efficiency, i.e., to allow speakers to say a lot in as few syllables as possible." While I'm not intimately familiar with the language, I know the making of Ithkuil involved a lot of mindbending reorganization of cognitive concepts. For example, if you're indoors, the spatial axes around which you organize your speech are placed with respect to the long axis of the room! (Of course, JohnQ freely admits that Ithkuil is extraordinarily difficult to learn, and has in fact created a somewhat simplified version, called Ilaksh, for those of us without superhuman vocal tracts.)
It can be argued that artlangers are just engelangers whose design goal is that of beauty, rather that something more conventionally associated with the words "design goal". It's a little like the distinction between architects and sculptors: you have people who are clearly one or the other, people who are mostly one with a little of the other, and people like Michelangelo or Maya Lin who straddle the boundary so well that no one ever finishes arguing about which category they fall into. (And, as good linguists, we have no problem with this, knowing that strict definitions are artificial constructions, and everything is better described in terms of generalizations from prototypes.)
Next up: the enmity, such as it is, between conlangs/conlangers and professional linguists / linguistics research.