"ACE (AdWords Campaign Experiments) is a free tool that makes it easier to test and precisely measure the impact of changes to your keywords, bids, ad groups and placements," that has just come out of a two month beta, Google stated on their Inside Adwords blog.
The program, which will be accessible inside Adwords accounts in the US over the next couple of weeks, allows advertisers to split test against running campaigns, etc. without compromising existing campaigns.
The feedback can then be compared directly and changes made to take advantage of any improved conversions. Previously much of this took a lot of set up and had to be deleted losing overall numbers.
Google sees this as a quicker way to improve CPA and provide an overall better experience for advertiser and user.
Other countries and languages will be rolled out in the coming months.