Mass Effect Team Assault is a FPS based off of BioWare's Mass Effect series. The game was in development in 2010. It was supposed to be a standalone title, possibly even a downloadable game. That idea was scrapped in favor of it being added to Mass Effect 3's multiplayer. Mass Effect Team Assault was eventually canceled all together as BioWare opted for Galaxy at War instead.
Mass Effect Team Assault came to light in the behind-the-scenes iPad app about the ME3 development process, The Final Hours of Mass Effect 3. Other details in the app reveal ME: Team Assault underwent four months of development, resulting in a prototype build in early 2010. The game would offer different perspectives from soldiers fighting in various battles from ME3.
I assume it never came to be since BioWare spent so much time making 16 unique, and totally different Mass Effect 3 endings. (Too soon?)
Image via Kotaku