The Rifter publishes a wide variety of game content under Palladium Books in-house dice mechanic system, coined the Megaversal System.
My experience in publishing material with Palladium Books was mediocre, for reasons I won't discuss. I'd recommend you look over their publishing agreement before writing/submitting content. The company is notorious for making changes to what their freelancers produce (and such I might add, is within their right via their publishing agreement).
You can take a closer look at what they are looking for in regards to writing submissions Here and their freelancer agreement is here.
Note: Submissions Open intends to be a freelancer's resource for the RPG Industry. If you're a publisher or game creator and interested in promoting a need for freelance writers or artists, drop me a line and I'll post your company data here on this blog. If you're a writer/artist looking for gigs click away.
Disclosure: The banner below includes my affiliate identification. I receive a token % if you purchase something and doing so supports this humble blog-thank you.