I guess before we think of ideas, lets get the setting. So do you guys want...
1. Pre Mass Effect.
2. During Mass Effect.
3. Post Mass Effect, Pre Mass Effect 2 (I'll count this as the 2 years while Commander Shepard was considered KIA.)
4. During Mass Effect 2
5. Post Mass Effect 2, Pre Mass Effect 3
6. During Mass Effect 3
7. Post Mass Effect 3
Restrictions
1. We can't use any of the Normandy Crew directly. This means that you cannot personally know Commander Shepard, you can however know of him obviously. If you're a pilot, you could have met Joker at flight school. You could have battled with Shepard in the past but not be a personal friend, just a soldier on the field. Some of the characters that will (if time allows it) make an appearance are: Admiral Hackett, Captain Anderson, Citadel Council.
2. You can play any race; Human, Salarian, Turian, Krogan, Drell, Hanar, Asari, etc. However, we don't need another Blasto. Combat roles should be restricted to those we've actually seen in combat (ME3 Multiplayer is a good example).
3. Based on time; (Anything pre ME3 Ending) Fame will be limited. There has to be a reason you wouldn't have been heard of. If it's post, the sky is the limit on fame. You could have single handedly wiped out a platoon of angry Batarians and saved the council.
Basic ideas
1.) New Frigate; Will have one of the participants as the ship captain. The other participants will either be members of the crew or people met (enemies or friendlies). Conflict: N/A
2.) Colony; A colony is under attack by Reaper forces. Alliance marines are fighting back. Takes place during ME3. All events take place either on world or in space around the planet.
3.) Gang War; Blue Suns, Eclipse, and Blood Pack conflict. Players take up roles as a member of one of the three gangs, civilians of omega, aria's goons, considering spectre of undecided race. Takes place pre mass effect 2.
4.) N7 Missions; A form of Roleplay on the Multiplayer of Mass Effect 3. Players take up the role of any combat race and form a temporary team to combat the reapers. Proposed this idea before, not enough support. Takes place during Mass Effect 3.
5.) First Contact War; Restricted to just Turians / Humans. The Humans just made contact with their first alien race, the Turians. Players will take up roles as either Turian Military or Human Military (gonna guess this one gets no votes).
Other ideas are still welcome; just making a path for people to take guesses on.