Retina is a network security scanner similar to Nessus. It had a rough time competing early in its career but recently has made a resurgence. I believe the government somewhat propped it up from dying, but whatever the case it has been revamped and is now a competitor with Nessus. It does all the same types of things other scanners do and is a pretty decent tool.
I've evaluated Nessus and multiple other products. I'd say Retina is right there with Nessus. At a certain point, it's not about if the product "finds" more vulnerabilities, it's about how easy it is for the end user. All scanners right now find about the same amount of vulnerabilities, but some are harder for users to use. Retina has a pretty well-designed user interface.
If you have an enterprise network, this is a tool that you're going to want to utilize, especially if you have employees that are not experts. The point of tools like this is to make an advanced task easy enough for a non-advanced user to do. Retina achieves this task, making it easier to do advanced things. It will also save companies money as they will not need to hire multiple experts.