The adjective simultaneous describes something that is done at the same time as something else. "The teachers all assigned simultaneous projects to the students that week. The kids were grumbling and sleep-deprived due to the grind."
The Latin root of simultaneous is simul, which also means "at the same time." One way to remember this word is to think of simulcast programs that are simultaneously available through different television networks, radio stations or Web sites — so you can catch that concert on TV while your friend is listening to it on his car radio.