The Gemini Effect is a special weapon of the game Star Trek: Armada. It is cast onto a specific ship and effectively clones it. The copy will remain for a while, actually dealing damage and receiving damage (can also be destroyed). The only difference between the clone and the original is, that the clone will have no special weapon energy, so it will not cast any special abilities. It is researched at the Science Station. The Gemini Effect in action looks like this:

This special weapon can only be cast onto friendly ships.

The Gemini Effect is also used by the campaign ship Premonition.

This special weapon can be misused by recycling the clones of the ships the Gemini Effect was used on to gain additional dilithium. Used on tier one units (everything built by Starbases and Tier 1 Yards) there is enough time for the special weapon effect to not wear of until the unit is deconstructed. In order to gain the formerly (for the original) invested Dilithium this requires working quickly and doing it in the vicinity of the entrance of an unoccupied yard. Basically it allows the player to generate Dilithium from nothing.

Similarly to the Money for Nothing concept you can achieve using Phoenixes for free. Just clone a Phoenix, withdraw the original and send the copy into battle. It can be used, as the Rift Creator does not need any special weapon energy. If you reach your target within the 30 seconds time interval, it basically gives you Phoenixes for free. This does not apply to the Jach'eng's Shockwave as it needs special weapon energy, which is not cloned along with the ship.