Whats the difference between "vCenter Converter Standalone" and "Converter Installer for Windows"

Firstly, apolgies for the noob questions.  We have spent days searching through the bewildering number of documents and products.

We have a vSphere 5 essentials installation.

The next step is to work out how to import physical CentOs and BSD machines into VMs.

According to this page: https://www.vmware.com/tryvmware/p/activate.php?p=converter

There are serveral different products:

1. VMware vCenter Converter Standalone
2. Converter Installer for Windows
3. Converter Installer for Linux

Questions:

1. What is the difference between these?
2. Do we need all 3?
3. Does the third product need to be installed on each physical unix machine which needs to be converted?
4. Can we do the conversion without vCenter, which we dont have as we dont have many of the pre-requisits (such as windows domain controller, databases, spare server etc)?

Many thanks to this excellent community.