Huh. Mirror Universe ships can seperate. Never saw that before; wonder if it was part of the season 11 update.
No seriously what is that?
Star Trek Online.
You can currently make characters in one of three factions; the Federation, the Klingon Empire, or the Romulan Republic. Feds and Klinks have different stories at the start, but they eventually merge together. Romulans have their own story at the start too, but you ally with one of the other factions early on, and then you follow the story of whichever you chose.
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It's free to play. There's a cash shop, and most of the best stuff is in it, but you can exchange in-game currency (dilithium) for cash shop currency anyway, so it's more pay-to-avoid-grinding than pay-to-win. They occasionally do free giveaways as part of events too.
They also occasionally *** up and send out free codes to people that shouldn't even be getting them, so that's kinda like having a lottery you're automatically entered in. I got a tier-6 (current highest) exploration cruiser from one such error.
If you don't wanna use the Arc launcher (I recommend you never use it, unless they do another giveaway where you have to log in through Arc to claim), you could probably find the old standalone launcher through Google, or you can get it on Steam.