You will find several tools developed by engineers to help in making life much easier for adminstrator or engineers alike. Some tools provide things like a GUI front for some of the common PowerCLI commands while some are load generator for a VDI POC or Test. Of course since this is a tool created by an engineer and not by a company, it is not a supported tool. It will be your own risk using them and supporting them.
A new tool was release on 2nd Mar named VCS to VCSA Converter. The name already tells it all. VCS is our vCenter Server while VCSA is vCenter Server Appliance. With each release of vSphere, there have been more and more improvement for the VCSA to match what VCS can do. With the recent announcement of vSphere 6, VCSA has already catched up if not all the features of VCS.
With this tool, you will be able to to move your VCS which is on Windows to a VCSA. Why would you want to do that you might ask? Well the reason is simple, cost and manageability. In terms of cost, you will save on your external database and Windows OS cost. In terms of manageability, it much easier to handle a vApp than to handle a Windows OS and a Databases separately (or as one depending how you deploy it).
Before going into too much joy, there are a few things that this tools migrate and not everything (almost all); vCenter database, roles, permissions, privileges, certificates and inventory service. You will see that metrics data is not part of the migration which means that need to be collected over time.