DC's Legends of Tomorrow accidentally end up on Earth 100 (which is where the events of the 100 take place) right before S3 E07 and without the whole Alie problem going on. The legends are the group at the end of season 5 plus Charlie and without Mick's daughter (Zari, Nate, Charlie, Behrad, Constantine, Ava, Mick, Sara, Astra).
This crossover wasn't originally my idea, but I'll try to stay true to most events and characters.