Looks for normal Amazon affiliate links and switches the www with smile so the affiliate can still get the referral and the customer can still donate to their cause.
More information http://thomasloughlin.com/amazon-smile-amazons-affiliate-program/
The plugin itself is doing a regex to find an affiliate link and then replacing the www. Very small.
It’s pretty simple to run, just drop it in the plugin directory and activate that’s all it takes.