The Frohmage Filter from Ohm Studio is a handy filter that you can use to effectively tweak just about any sound for the better.
“Is this a toy? Certainly not. It may be generously offered for free, however it’s also a powerful filter that you will be likely to use very frequently in your tracks. Far from being cheesy, as its unique interface suggests at first sight, Frohmage delivers warmth, dirt and much more at a professional audio quality.”
Freeware for Windows and Mac.