Mixxx - The Best Free DJ App
I love freeware, open source and all things free, so I'll share some of the best music and audio freeware to help you make fresh music and mixes. Starting with Mixxx, who just released their new version 2 of their DJ software for anyone who likes to play music or throw a party.

The app may be free but this does't mean it lacks features. It can be used with an external sound card and mixer or it can mix with your native audio interface. The interface is intuitive and user friendly, amateurs and pros will find it easy to use and navigate. Different skins are also included. Supporting most common audio formats MP3, M4A/AAC, Ogg Vorbis, Opus, FLAC, WAVE, and AIFF, Mixx will play almost any track in your library. The library manager is very powerful and lets you easy browse it by genres, BPM, or create playlists. Some other major features are complex routing, time stretch and vinyl emulation, beat looping, easy syncing, hot cues and of course EQ with effects and a crossfader.
All you'll ever need to play and mix like a pro.
There's a extended manual if you are new to concepts like mixing, beat matching and how to use the interface, read it here. Another great thing is that Mixxx is crossplatform, it runs on Windows, Mac and Linux.