There are many tools testers use for reviewing web applications every day. In daily tasks some of the most used applications include virtual machine for testing in different enviroments and a screen capturing application for reporting bugs with screenshots. I will present you couple of free tools for Windows which I use all the time.
Dexpot is a great virtual desktop tool, which allows you to switch between desktops easily. I usually have a virtual machine located in one of the desktops, so I can easily switch between the operating system in the virtual machine and the one in which I run the virtual machine. With Dexpot you can easily configure every desktop separately, move applications from one desktop to another and many more.
Virtual Pc is a free virtualization suite from Microsoft. It allows you to run different versions of Windows operating systems. In Virtual PC, you can use a free trial image of operating systems which you can download on Microsoft's website. I use Virtual PC often for testing in IE6, FF2 and Safari browsers.
Jing is a free screen capturing application from the makers of SnagIt. Jing allows basic operations like adding text, arrows, marking area, highlighting, and also allows making videos too. By the number of operations and quality it's far from SnagIt, which is an awesome screen capturing application, but it is more than enough for basic screen capturing operations.
Taskbar Shuffle is a very small, but usefull free utility which let's you drag and drop your Windows taskbar buttons to rearrange them. It can be very usefull when you have a ton of opened applications in your taskbar and you need to order them in some way.