How can I create a "reputation" system similar to StackOverflow using Rails?

I have users in my system and I want to create a reputation system where they begin to accumulate points based on a few, simpler inputs:

• The ratings of their reviews
• The number of reviews they have
• The number of followers

I don't need it to be super complex, just functional and believable. I am seeki开发者_高级运维ng help both on the "math" side, but also if there are gems they do pieces of it on the user-interface and data-model side.

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I would take a look at thumbs_up, I looked into it for a recent project and now wished we had used it instead of a different gem. Seems pretty straightforward.

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While it's not a Rails specific book and more conceptual, I recommend the book 'Building Web Reputation Systems.' http://www.amazon.com/Building-Reputation-Systems-Randy-Farmer/dp/059615979X/ref=sr_1_1?ie=UTF8&s=books&qid=1303234014&sr=8-1

Depending on what you're trying to do, lots of planning goes underneath them and the book talks a lot about the process along with other examples from Yahoo and soforth.