Gamipress is GREAT!

This is a really flexible plugin with add-ons (for free and fee) that extend it even more. It can take a bit to understand it all (because it has a lot of bells and whistles). However once you do, it is super powerful.

I love all of the features, flexibility, instructions/documentation, case studies (e.g., php snippets to help customize it even more). It’s a solid plugin.