VKernel, now part of Dell, is a perennial leader in producing free tools. VKernel vOPS Server Explorer is a great combination of several of the company's existing free tools, in a single virtual appliance.
VKernel vOPS Server Explorer combines Environment Explorer for inventory and performance, vSCOPE Explorer to identify VM health and capacity issues and SearchMyVM for virtual infrastructure query. These capabilities -- now merged in a single, free virtual appliance deployment with vKernel vOPS -- promptly provide an overview of what the vSphere infrastructure looks like and where potential performance issues are.
When you install it, the new vKernel vOPS Server Monitor is a full installation of vOPS, vKernel's commercial product. If you did choose to unlock it, either with a trial key or by purchasing it, the appliance still has all the data that has been collected since installation available for analysis.