Years ago, Acid (I forget who made it) used to have great features for beatmatching tracks and pitch shifting. It wasn't the best DAW by any means but it seemed to have been designed for making mashups.
Acid was pretty ground-breaking at the time it came out, I think a lot of beat-matching features in modern DAWs was inspired by what Acid did. It was made buy Sonic Foundry who then sold it to Sony - http://www.sonycreativesoftware.com/acidsoftware
I have an unusual amount of knowledge about Acid since a friend of mine originally created it (he left Sonic Foundry to work on audio software at Apple the last time I talked to him) and I used it to produce two albums back in the day.
