jsCompShaper by jsAudio is great sounding free soft-knee compressor/waveshaper plugin. Some of its features include the ability to morph between soft-knee compression and waveshaping, pre-/post-emphasis filtering (similar to a side-chain filter), support of parallel compression, oversampling (1x-16x), analog style Attack control and more.
This thing is a BEAST i.e. in a drum track if you seriously want to “pump” things up. Check an example below: