Rocket Age takes you back to the sci-fi era as envisioned in classic sci-fi tales. Where every planet was habitable and filled with strange civilizations and adventure, travelling between planets took a day or two at most, and rayguns were standard-issue. They've adapted the game to work with 5th edition Dungeons & Dragons and have put the book up on Kickstarter.
From the campaign:
Welcome to the 1938 that never was and the Solar System that should have been!
Rocket Age is a radium punk sci-fi game of exploring the Solar System, fighting Nazis, Stalinists, aliens, and the bizarre environments of nine planets (yes nine, it is 1938 and Pluto is still a full fledged planet). It is a game of ancient ruins on Mars, the steaming jungles of Venus, strange life in the clouds of Jupiter, RAY guns, chromed rocket ships, radium fuel, hot exhaust, and fins. So many fins on things you didn't know you could put fins on.
The setting is a kitchen sink sandbox for you to set your games in. Want to be the brave explorer discovering lost civilizations and new wonders? We have that on Venus, Mars, Jupiter, the Jovian Moons, and more. Looking for a daring game of brinksmanship as you battle agents of foreign powers (even alien nations)? Choose whom you want to fight and who you want to fight for, be they Americans, Nazis, Soviets, Martian princes, or the enigmatic Europans.
The campaign's about 3/5 of the way to its goal with 28 days left to go.