.NET Repair Kit

Eventually, your .NET Framework installation will need updating.  .NET updates, especially those security-critical ones, have been known to endlessly fail and get stuck in the Windows Update queue.  This happened to a computer I was working on today, so I looked up how to fix the problem.  I found a very helpful post on Microsoft Answers that contained a link to a collection of utilities that fixes the problem.  It does so by completely uninstalling all versions of the Framework, then reinstalling them.  I put those four programs into one ZIP archive, which I recommend you keep on hand in case this problem happens to you.