Ars Magica is a pen and paper RPG first published in 1987, which makes it fairly oldschool. It is currently in its fifth edition. The setting is another pseudo-historically accurate depiction of High Middle Ages Europe but this time with MAGIC and WIZARDS, so that makes it totally unique! In fact, the game setting and geography is so uniquely, accurately European that it might as well be called Europe, but instead they just called it Mythic Europe! In order to help hammer that "authentic" Old World feeling directly into your skull, the game is quite liberal with using medieval Latin for a number of game related terms.
Ars Magica was among the first RPGs to use a "troupe" approach to roleplaying. As opposed to having a single GM responsible for all story-telling and control of NPCs, multiple players could instead share the burden, taking up the mantle of "Story Guide" at different parts of the adventure, or run their own side-stories, or even take on the role of story adversaries when appropriate. Given the nature of this narrative and playing style it was not uncommon for a single player to have multiple other characters spread out between multiple stories, sometimes simultaneously, and maybe even in opposition to some of that player's other characters! Although more recent editions did begin to de–emphasize this troupe-style play in favor of the more traditional mono-GM, the fifth edition rulebook does still have rules for troupe play, though they are stashed at the back of the book as an optional rule.
A player's main character in Ars Magica will generally always be a mage, and the multiple magi in the party will all be members of the Order of Hermes. The Order of Hermes is like the United Nations for wizards, which was formed after the fall of the Roman Empire to try to put the kibosh on the sort of destructive and retarded world-breaking things that wizards are generally known to do everywhere, all the time in other settings. Thus the Wizard's Union that is the Order of Hermes pretty much monopolizes magic by killing any "gifted" they come across who refuse to submit to their authority. The Order of Hermes is divided into thirteen different Tribunals, each which oversees a different geographic region of Mythic Europe. The Order is also divided into twelve separate Houses, each representing a distinct magical lineage. And with myth and wizards being the game world's defining feature -since without them, it would just be Regular Europe- it is no surprise that the magic system of Ars Magica is fairly well fleshed-out. Hermetic Magic consists of 15 Arts, which is divided into 5 Techniques and 10 Forms. "Gifted" users of magic can thus manipulate the world around them by using techniques to verb something's nouns. Basically, Five By Ten Magic. There are actually several systems of magic in-universe, each practiced by a different type of wizard, but the Hermetic one just mentioned is usually top-dog for lore and mechanical reasons, and only people who practice it can join the Order, those that don't are usually regarded as beneath notice.
Individual Magi themselves will often congregate with one another in special outposts called Covenants. Here the magi live, study, research and engage in other wizardly pursuits. Also living at the Covenant will be a number of Companions. These Companions will often also be player characters; they are usually "mundane" (unable to use magic), however they have other skills which make them useful in different ways that magi, aloof in their pursuits of magic, will generally have less time to dedicate to, though some Companions can use some of the other, weaker types of magic available in the setting. Lastly, there are the grogs. Grog is a catchall term, akin to serf, for members of the peasantry who perform low-skill and unskilled work at the Covenant. The Covenant will generally have many grogs, and many grogs is referred to as a "turb" of grogs. Grogs are generally treated as shared characters between all players at the Covenant, as viable rules for playing as a grog did not appear until third edition. Because of the many possible player characters and all their comings and goings as they adventure throughout the Tribunals of Mythic Europe, it is often joked that the main character in a game of Ars Magica is actually the Covenant itself.
Ars Magica was developed by Jonathan Tweet and Mark Rein·Hagen, and first published by Lion Rampant in 1987. A second edition would be published before Lion Rampant would merge with White Wolf Magazine to form White Wolf Publishing in 1991. In 1994 the game was sold to Wizards of the Coast, who would go on to create the fourth edition two years before selling the game's rights to Atlas Games in 1996. The fifth edition was released in 2004; it was the most substantial overhaul the game had received to date, and made many long-overdue improvements to the combat, experience, and character creation process.