.NET-like framework for native C++ with precise generational mark-and-sweep GC  which gives better performance than boost::shared_ptr especially in multithreaded apps. Speed difference is most profound on server boxes with multiple CPUs. I've also created a similar library for GCC - Managed C++ for GCC (MCP).
Also found several C# language design oversights  causing weird and undesired side effects to programmers, as well as numerous framework bugs    (that's to be expected considering the size of the framework).
But the biggest of all, finding a critical bug in WOW64. Microsoft OS team stuffed up the WOW64 design of their Windows OS during the design phase of Windows XP x64. They've said it's too costly to change now (design flaws are always the most costly) and would perhaps try to fix it for Windows 8 (we'll see about that). I was surprised that the bug went unnoticed by the brightest people (Boehm GC guys would've seen it for sure) in the world for 11 years before I came along and root caused it in about a day.
Feel free to visit my Website.
And my Blog.