"Agone", a 1999 role-playing game of "baroque fantasy". It was created by Multisim, which was a big player in the French RPGs of the time. The game had a great success until 2003, when Multisim ceased to exist, ending the line.
This game is actually the adaptation of a literary universe - Mathieu Gaborit's Royaumes Crépusculaires (Twilight Realms) also known as the Harmonde universe. It first appeared in his trilogy "Les Chroniques des Crépusculaires" (The Twilighter Chronicles), published from 1995 to 1996 (Souffre-Jour, Les Danseurs de Lorgol and Agone), before being compiled into a single-book, revised and augmented version in 1999. "Les Chroniques des Crépusculaires" is quite famous for being one of the very first "French fantasy" proper, part of what was known as the "Mnémos generation", the boom of French fantasy in the 90s thanks to the Mnémos publishing house. [Before, in literature, fantasy was solely the importation and/or translation of English-speaking works, with French authors having to bend their works to fit other genre etiquettes such as "sci-fi" or "fantastique"].
The world of the "Royaumes Crépusculaires" was also explored in another fantasy series of Gaborit, "Abyme", originally a 1996-97 duology (Aux Ombres d'Abyme and La Romance du démiurge) before being "reforged" into a single book from 2000 onward. The game "Agone" is both based on "Crépusculaire" and "Abyme", which notably led to the creation of inter-media works, such as 2009's "Abyme: Le Guide de la Cité des Ombres", a multi-authored "official guide" to the city of Abyme that can serve as material for the role-playing game or a companion book to the novel series. Mathieu Gaborit himself participated in the design and creation of the "Agone" game - though the man behind it was Sébastien Célerin.
The basic principle is simple. The player can be as much a human as a "saisonin" - basically a traditional fantasy being (satyrs, minotaurs, giants, pixies, dwarves, gorgons and more) but here oriented onto one of the four seasons - but they will be one of "Les Inspirés". The Inspired ones - those gifted with Inspiration, or "The Flame", which notably allows them to reach the Magical Arts. Quite literal magical arts, as here magic comes in four great families of crafts, each centered around a different artform. La Geste (poetry), la Cyse (sculpture), le Décorum (painting) and l'Accord (music).
And the main goal of the game is for the players, as Inspirés, to fight off the plans of The Mask, aka "The Master of Seemings" (Le Maître du Semblant), the Twilight Realm's equivalent of the devil. The world of the game was created by four divine beings known as the four Muses - aligned on the four seasons and four arts. Today they are gone from the world and it is in no small part due to the machinations of The Mask, who was an attempt by the Muses to create a fifth divine being equal to them, but only resulted in creating a malevolent, manipulative eternal being who now is seeking to remove all magic and wonders from the universe (thus plunged in a "twilight" as the Mask seems to remove the "Flame" out of living people). The players notably can bring on a "Flamboyance" by restoring fully magic to the entirety of the world.
But it is not easy as the Mask already has a solid grip onto the world - he owns Autumn and its seasonal beings (resulting in it being a "cursed season" of one month only), and he corrupted one sub-type of Accord magic (the clavecin-caused spells) into a perverted magic, le Faux-Accord.
After the publishing of the core-book, Agone grew out into fifteen supplements, each exploring and expanding on a different aspect of the Gaborit-created universe. This included maps and bestiaries, exploration of the magic types and various campaign scenarios, and the "Cahiers Gris" duology (about the various organizations and secrets within each of the kingdoms of the Twilight Realms).
One of the supplements is notorious for many reasons: "Abyme", centered around the city of Abyme (setting of the second series written by Gaborit, as said above). Not only was it the biggest supplement, literaly, but it also offered a simplified alternative game system - meaning that it could act as either a supplement to "Agone", OR as a different game on its own.
The core-book was translated by Multisim in English in 2001. They also published a Gamemaster Pack, as well as the translation of three supplements (the first Cahiers Gris ; the Art de la Magie supplement, under the name Grimoire, and the Monarque des Jonquilles supplement, as "King of Springs").
After Multisim ceased to exist, the fate of Agone remained up in the air. There were two more supplements planned but not published (Le Guide Abymois ; and an atlas of the Royaumes Crépusculaires). Ubik reprinted the core book in 2004, but couldn't go further due to juridic disputes over the ownership of the rights to the game. From 2004 onward the Agone community mainly survived through a fanzine called "Souffre-Jour", to which some of the authors who participated to the supplements provided content - it lasted for nine issues. [Before it there was, up until 2002, an official "numeric gazette" you could buy, called L'Inspiré and which was published online as PDFs acting as "mini-supplements" - there were only three issues of it].
Despite all this, one of the unplanned supplements managed to be brought back! Remember "Abyme, le guide de la Cité des Ombres" I just talked about? It is actually a re-adaptation of the original "Guide Abymois" supplement. There was also a publication by Coralie David of various short stories published in the supplements - written by either Mathieu Gaborit or by Raphaël Granier de Cassagnac, David compiled and re-edited them to publish in 2016 the anthology "La Confrérie des Bossus" (The Brotherhood of the Hunchbacks).
