Headline Split Tester allows you to have two competing headlines for blog posts. They are randomly shown until one headline wins.
Installation is easy
headline-split-testfolder to the
This sometimes conflicts with social media tracking systems that (foolishly) use things like the Post title rather than the GUID to track activity around a post. If this is a problem, go into the settings page in your admin screen and you can configure it to not use the alternate headline on the page, only on the link to the page. This means that when a post wins, you would be best served by changing the post title, although that might mess up your social media mojo as well. Alas.