If you know me, you'll know that I love exploring new PIM (personal information manager) software tools. One of my favourite categories of such software is mind mapping, but there are very few mind map tools that are any good and which don't cost lots of money.
So imagine my delight to come across Blumind, which you can get from http://blumind.org. It's free, it's only a 0.6 MB download, and it runs under Windows XP and above. You may need .NET Framework v2.0, depending on which version of Windows you're running, but you've probably got that already.
You can choose to download the installable or the portable version. Portable apps are great, as they give you a handy way to try out the program without increasing the size of your registry. If you subsequently decide that you like the program, you can then go for the full install.