Windows and Microsoft.
I explored and worked with Win32 api's in C, toyed with MFC, then moved on to Windows Forms.
Web Development with C#, ASP.NET-MVC, ExtJS 4
The bulk of my work at my current job has been planning, developing and maintaing a rewrite of a massive healthcare application with several teams.
The Weird World of Perl
My tryst with the Linux Kernel:
While soul seraching on wiki.osdev.org .I started lurking at the linux mailing lists and managed to scrounge up some work. I managed to submit a few patches to the kernel. I stopped for a bit but plan to get back and try to get to more serious work.