Multiple improvements to the BCL to reduce usage of non generic collections and use faster string comparisons.
Optimize large object cloning and boxing.
Multiple changes to bring mono closer to full PCL compatibility.
Sgen can now return memory to the system for
Many compiler fixes for async.
Improved FullAOT support for async.
NaCl build fixes and improvements.
WCF now has cookie support in .net 4.0.
Optimize Marshal.Read/Write methods to avoid a trip to unmanaged when needed.
Optimize LINQ with arrays.
Multiple fixes to the sgen's concurrent collector.