Spotifree is described as 'OS X app that automatically mutes ads on Spotify' and is an app in the Development category. There are five alternatives to Spotifree for a variety of platforms, including Windows, Linux, Online / Web-based, Google Chrome and Firefox. The best alternative is EZBlocker, which is both free and Open Source. Other great apps like Spotifree are SpotiShush (Free, Open Source), Smutefy (Free, Open Source), Blockify (Free, Open Source) and Spotify Ad Blocker (Free, Open Source).
Smutefy is a small menu bar application that automatically detects and mute Spotify ads. How it works? Spotify uses growl to show a notification when a song changes. Smutefy uses growl log to detect ads and automatically changes the audio interface to mute the ad.
Portable - put it anywhere, run it and forget about it. (And you might want to enable "Run on startup" from the tray icon) Works by muting only Spotify during ads. The sound of your other applications will keep working.