Hobo is useful when you're managing more than one virtual machine using Vagrant. It also gives you a GUI for creating basic Vagrantfiles to configure your virtual machines.
Hostbuddy is purely for helping you edit your /etc/hosts file. It lets you create groups of host entries and switch between them with just one click. This is useful if you're needing to switch between staging and production servers that use the same host name but different IP addresses.
VirtualHostX is used for hosting more than one website on your Mac at the same time. Previously, prior to version 7.0, VirtualHostX worked with the Apache server that is built into your Mac. With version 7.0, I made some big changes. Now, instead of your local web server, VHX creates a real Apache server using an Ubuntu virtual machine - managed with Vagrant and VirtualBox. This is useful because now Apple's system updates cannot interfere or mess up your web server configuration. It also lets you fully customize your web server with any software you want - since it's running independently of your Mac.
Does all of that make sense? Happy to answer any other questions you have.