Registry Cleaner will take care of searching in the Windows Registry for all kinds of incoherent information, surplus entries, inaccurate entries or indications that no longer work. This means, it cleans the registry of contents that can't be used for anything and that only slow down the system.
On the other hand, the Registry Compactor is the one in charge of speeding up the system registry to manage to make sure that it starts earlier, produces less errors or simply to make sure that everything works properly.
Thanks to RegSupreme it's possible to have these two excellent programs in the same application that has a really simple and understandable interface. Even though it's a long way away from the graphic innovations shown by more modern tools, the truth is that this is one of the best and most acknowledged in its field.