Starting September 1st 2011, Nintendo 3DS Ambassadors will be able to download 10 NES Virtual Console games. Then, before the end of 2011, Nintendo will provide Nintendo 3DS Ambassadors with 10 exclusive Game Boy Advance Virtual Console games.
The latest revisions to the 3DS line are - the 2DS, which was a budget version with no hinge or 3D effect, and the 'New 3DS' which is a more powerful model with additional buttons, and upcoming games that will be exclusive to it.
Nintendo 3DS games are only playable on Nintendo 3DS systems, and in order to play Nintendo 3DS games multiplayer, you require multiple Nintendo 3DS systems. However, Nintendo DS and DSiWare games that support multiplayer can be played using the Nintendo 3DS system.
It depends on which Nintendo console you are referring to. Nintendo 3DS games can only be played on the Nintendo 3DS, Nintendo 3DS XL and Nintendo 2DS. All other Nintendo consoles including the Nintendo DS and Nintendo DSi cannot play Nintendo 3DS games.