Twitter's new Promoted Tweet Carousel will allow advertisers to "curate multiple Tweets" all within a single swipeable ad unit. It's being made available as a limited trial Alpha in selected accounts in selected global markets. It looks interesting, and you may want to watch out for it.

We are excited to announce we’re beginning to test the Promoted Tweet Carousel, a new ad unit that gives marketers a rich canvas for brand storytelling using their own Tweets or Tweets about their brand by users, who have given permission to the brand Twitter Test Promoted Tweet Carousel [blog.twitter.com]