This week marks the 30th anniversary of Chaosium's Call of Cthulhu, and since its original publication, CoC has influenced generations of game designers and spawned the flourishing niche of Cthulhu Mythos gaming.
Perhaps the most recognizable spinoff of CoC is Delta Green. Created in 1997 by John Tynes, Dennis Detwiller, and Adam Scott Glancy, Delta Green brought he Cthulhu Mythos into the modern day, re-contextualizing the literary world of H. P. Lovecraft through a lens of conspiracy and paranoia. Players took on the role of agents of Delta Green, a rogue government agency protecting the United States from supernatural threats.
In 2008 Kenneth Hite reinvented both Mythos and investigative gaming with the release of Trail of Cthulhu, a roleplaying game using the GUMSHOE system. Eschewing the traditional period of the 1920s, Kenneth Hite transplanted the action on the 1930s, with the specter of war hanging over the East and West, and pulp and film noir dominating popular culture.
Arriving the same years as Delta Green, Cthulhu Live brought the Mythos into the world of live action roleplaying. Now in its 3rd edition and supporting a variety of pre-made scenarios, Cthulhu Live events have come to be a staple of conventions such as Origins and GenCon.
With Chaosium's recent decision to license CoC to 3rd party developers, the Mythos gaming genre continues to grow and mutate like the proverbial shoggoth. Do not attempt to envision what its next 30 years will bring. It'll be enough to drive you mad.