An animated show where there was this guy whose brother worked in the CIA. The guy was jobless despite having graduated from college, and pestered his brother to try and get him into the computer company said brother pretended to work at. The brother actually needed a "guinea pig" for the project he was working on, so he told the protagonist about his real identity.
Now, the main character was given a Star Trek like assignment of going to other worlds and coming back with research. The difference? All of the other worlds were different Earths from different realities. The CIA had him use their inter-reality portal to reach said realities, each one being a different episode. It was unable to pinpoint specific realities, however it could always return him to his own one. Because of this, once he came back to his home reality, he could never go back to the one he was researching, meaning that he would lose out on literally a world of research if he ran from a battle, and if he found paradise, he would be forced to leave.
The main antagonists of the series are The Nameless and an alien species that speaks another language humans dub as The Speechless. The Nameless is an organization that exists between every reality; in some, it's just a local gang, and in others, it literally consists of every human on the planet. This causes the protagonist to believe that somewhere in his own reality, The Nameless exist.
The Speechless, on the other hand, aren't even human. I suppose the best way of describing them would be flying zoras, but with a few insect qualities, too. They oppose the protagonist, however are attacked by The Nameless, too. When they come in contact, The Nameless always lose human qualities such as emotions and speech, becoming mental monsters.
In the finale, it's revealed that The Speechless act as a police force of sorts. Whenever the faulty portal from every episode is used, the reality he goes to becomes corrupted. Depending on how many different decisions away it is, it'll be more or less corrupted. Corrupted humans become The Nameless, and corrupted terrain is flat out gone.
I had a few unique ideas for the different realities, but one of my favorites was one that was constantly at war. The world was basically split into two factions, The Nameless being one and The Survivors being the other. Humans had evolved differently, and had slower reflexes, but higher strength. Because of this, they were unable to physically kill one another; the battle would just be too slow. Additionally, there were incredibly logical, but hadn't invented weapons. The battles of the war consisted of the two sides going up to eachother's faces and convincing the other side to commit suicide.