I was just reading through some articles to keep your system to the best of its performance and one point mentioned in all of them was to defragment your system and to clean the registry. So here are some open source softwares I found for this purpose.

Little Registry cleaner it is, the alternative open source windows registry cleaner.  Small in size, neat and easy to run. Basically removes obsolete and unwanted items that build up in the registry over time. Before cleaning the registry it also creates a backup of all your registry information  so that you can roll back if the registry cleaning causes some problem. Usually there wont be a need for it, but its just a precaution for those very few instances when something might go wrong.

Scan in progress