There is a lot of very good freeware available to Home PC users.  The following is a selection of ones I have found useful.
Anti-Virus
It's essential that your computer is protected from viruses.I recommend Avast 
Anti-Malware
Remove Malware and Spyware with Malwarebytes or SuperantiSpyware
Text Editor
Edit text files (like NotePad) and much much more - from Fookes software.
Image Editor
Adjust your photos and add weird and wonderful effects with Photofiltre or Irfanview.
PDF reader
Foxit PDF reader is a lightweight PDF reader with a lot of functions
Windows Shortcuts
Now includes Windows 10 and IE11
I've written a short document with some useful Windows shortcuts in it.  You can view it by clicking the link. Use Adobe to print it in Booklet form (double-sided)
Updated Dec 2015
Adobe Reader
If you can't view the document above, you need to install the free viewer from Adobe
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