Extraordinary Concentration( Complete Adventurer, p. 109)
Your mind is so focused that you can cast spells even while concentrating on another spell.
Concentration 15 ranks,
When concentrating to maintain a spell, you can make a Concentration check (DC 25 + spell level) to maintain concentration with just a move action. If you beat the DC by 10 or more, you can maintain concentration on the spell as a swift action (see Swift Actions and Immediate Actions, page 137). Using this ability is a free action, but if you fail the Concentration check, you lose concentration on the maintained spell and its effect ends. This feat does not give you the ability to maintain concentration on more than one spell at a time.
Concentrating on a spell is a standard action.