Magic Playlist - Get the playlist of your dreams based on a song
Youtube-DJ - Mix YouTube songs together
Spotalike - Spotify playlist with similar songs, according to Last.fm
Edjing - Discover edjing and edjing Pro, the most powerful DJ apps for music lovers! Mix on Android, Windows and iOS devices and record then share your DJ sets!
Playlist Machinery - Tools that help you create & organize your Spotify playlists
YOU.DJ - Mix SoundCloud music and Youtube videos live in your browser.