We've implement e-junki both for our payment engine and affiliate scheme. http://status2k.com
Status2k is a server monitoring and administration script allowing you to monitor your server. Not only is it a simple tool for clients to check on how the server is preforming its also a valuable administrative tool allowing admins to check log files, bandwidth usage, high load processes and much more all via a web based control panel. Status2k is coded entirely in PHP and can be setup on most servers in under 5 minutes.
The Status2k team