The new version of Pioneer DJ's rekordbox has added an easier way to mix in key. The new 'traffic light' system highlights tracks that are suitable to play next, if you want your music to match harmonically. Despite being called a 'traffic light' system, it only seems to use the colour green, rather than orange and red for tracks that may clash slightly and tracks that don't work at all.
Either way, it's another way to assist DJs in their mixing. It's not clear how it will translate, or translate at all to CDJs, but as they already feature a key matching system it's unlikely to change things too much – the new system works in both Performance and Export mode.
The new 5.4.0 beta is available now and can be downloaded here, but as always, backup your collection before you start playing around with unstable software. Other new features include a 'library protection' system to stop anyone editing your collection. rekordbox dj's evolution is happening at a fast pace, with the latest version adding control of lighting via external DMX boxes.