Windows only: MouseZoom is a tiny portable tool that functions both as a screen magnifier and a colour picker.
Whether you've been looking for a detailed colour picker or you're just looking for a way to zoom in and track progress on a Windows machine, MouseZoom is a free and tiny solution. When MouseZoom is open anywhere your cursor goes you get both a magnified view and detailed colour information. You can turn off the colour picker if you don't need it and zooming is incremental from 2x to 50x. Upon startup there is a small nag screen urging you to register the tool with the creator, as there is no fee it's the web equivalent of postcardware. MouseZoom is freeware, Windows only.