Requirements:

a UNIX type server
Perl 5 and an e-mail program installed on the server
permission to run CGI scripts on the server and a FTP access

Features (version 1.3):

easy to install and configure, FREE installation with purchase
supports both banners (all sizes) and text ads!
uses confirmation e-mail to prevent unsolicited signups
pay your affiliates a flat commission or "percent of the order value"
Admin area with easy tools to view/edit affiliate program, affiliate info, banners, text ads, add/reset earnings, use an optional field to collect additional information from affiliates, e-mail utility and more!
User area with user editor and HTML code generator
Easy to implement into your existing store/purchase forms

Easy integration with 2checkout, PayPal (uses "Instant Payment Notification" so a Premier or Business PayPal account is required - upgrade from Personal account is free, more info at PayPal) and many other 3rd party credit card processors/shopping carts!
Supports Search Engine friendly links for easy spidering and PageRank increase Possibility to automatically add a small fee to every new user that signs up (so you can attract affiliates with "Get $X just for signing up!")
Credit your affiliates for recruiting new webmasters!
Easy to translate to any language!
Friendly interface