Not really. .net apps have already been running on Mono, with varying success; there are also cross-platform apps built on .net - none of this should change significantly.<p>As for unmanaged apps - this changes nothing.<p>Two things could happen: a) the open-sourced .net will allow for better implementations on other platforms, and/or b) MS will later step in as a patent troll and try to undermine Mono this way, SCO-style. While option B seems unlikely (the open-sourced code seems to be licensed quite freely), MS has played the Embrace-Extend-Exterminate card too many times for me to be entirely trustworthy.
With the exception of wine.<p>Short answer: No.<p>Longer answer: Probably not. Anything that P/Invokes native code (regardless if it's a system dll, or the apps own dlls) it will just not run. They will crash/throw exceptions when called. Since these apps won't expect themselves to be running on a non-windows operating system the exceptions won't be caught and crash. This will probably include many, many 3rd party controls.
As of today and as has been the case for several year now, many Win32 based Windows softwares/games already run just fine on Linux and OSX thanks to Wine:<p><a href="https://appdb.winehq.org/" rel="nofollow">https://appdb.winehq.org/</a>