The most memorable of the organization of the games.

Umbrella the most memorable from school)

H. A. R. M., Majestic 12, Cabal, Armacham, the Brotherhood of NOD.

Enclave
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CELL
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Cerberus
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Alliance
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Institute
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I only remember Mass Effect' - native Alliance and Cerberus.

Enclave, Brotherhood Of Steel, Monolith, Duty, Armacham Teknoledzhi, Abstergo Industries.

Abstergo,the Enclave, Brotherhood of Steel, Subway, the Institute,Cerberus,the Alliance,the Dark brotherhood, Morag Tong, thieves Guild, Companions, dawnguard, Sharif industries, Eurocorp, Black Mesa, Hyperion,Fema,F. E. A. R.,forgot, Vault-Tec,Fontaine Futuristics. Now all seems more do not remember.

Wait for an official Poros from PG, pass. or such already was?

Corporation Fontaine from Bioshok
The enclave from Fallout
Umbrella of Rezika.

Majestic 12 - Deus Ex
G22 - Alpha Protocol

I love a good secured secret of the organization.

And
UED (Starcraft)
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XCOM
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