REMnux is designed for running services that are useful to emulate within an isolated laboratory environment when performing behavioral malware analysis. As part of this process, the analyst typically infects another laboratory system with the malware sample and directs potentially-malicious connections to the REMnux system that's listening on the appropriate ports.
You can learn about malware analysis techniques that make use of the tools installed and pre-configured on REMnux by taking my course on Reverse-Engineering Malware (REM) at SANS Institute.
Originally released in 2010, REMnux has been updated to version 2 in 2011.
You can download the REMnux distribution as a VMware virtual appliance archive and also as an ISO image of a Live CD. MD5 has values of the latest files are: