You can take a look at various things here, and you can find the Imagine Role Playing Discord (where this game will be doing voice) here: https://discord.gg/qeTA74B26z
You can find a discussion about what a West Marches game is with a google search, but a good description can be found here: https://dungeonsanddragonsfan.com/dnd-west-marches-campaign/
Imagine is a role playing game system that has been around for quite some time, but has not been talked about much. You can find a written review here: https://www.rpg.net/reviews/archive/classic/rev_5517.phtml
And a youtube review here: https://www.youtube.com/watch?v=nn1Epv09Yx8
And you can find their official website (with books in pdf or physical form) here: https://role-playing.com/
The world of Negir'Tan was once a conquered world, where the Overseers ruled over vast swathes of the land, keeping the peoples there subjugated. But their rule ended centuries ago, when they packed up into their ships and returned to the stars from whence they came. The decision was not made without cause, for shortly after they left, a transformative mist settled upon the surface of the world, twisting both man and beast into ravening creatures bereft of reason. Many were lost, but some few survivors managed to make it to the sky-islands the Overseers left behind, to begin re-establishing civilization with what they could.
Centuries have passed since then, and now, the Wizard's Guild of Bekent has announced an amazing discovery: They have perfected an enchantment that will allows people to travel in the Baleful Mist for a period of time without suffering it's corruption. They have sent out the call far and wide for adventurers stoic enough to brave a return to the surface, to reclaim the resources and treasures that were left behind those centuries ago, and perhaps..... to clear the Mist, so that people can return to the surface.