&gt; Ableton, Cubase, everything from NativeInstruments, including sample libraries which sometimes are the reason why you need KONTAKT, and not some other sampler. U-he Zebra. Hundreds of various VST plugins from different developers: reverbs, phasers, limiters, etc. Often this stuff is quite trivial, but there just is some amount of domain knowledge which random opensource developer just doesn&#x27;t possess. That&#x27;s why free stuff available sucks or even doesn&#x27;t exist.<p>Ardour is the basis for Harrison consoles which are fairly well respected. I would also comment that open source audio plugins tend to look much worse than they actually sound.  Totally vanilla UI for an audio plugin doesn&#x27;t inspire much confidence in the audio quality (watch Century of the Self for more on that).  I&#x27;d personally like to see a real contender for open source clone of Propellerhead Reason.  Cubase is far less programming work than Reason IMHO.<p>Sample libraries aren&#x27;t &quot;source code&quot; and in that sense they cannot be truly &quot;open sourced&quot;.  Creative content such as this is more on the Creative Commons side of matters -- for better or worse.