Larry Osterman started a series of posts on his blog, where he talks about the stuff he was doing in the past. So, I thought it would be a good idea to talk about suff I did at Microsoft.
One of the things that I am really proud about, is a feature I implemented for Exchange2009, which is called "Call Answering Rules". The best way to explain this, is to think about it as the equivalent of the Exchange/Outlook rules, but for your phone. This allows you to create rules that govern how incoming calls to your phone are routed.
Some of the examples of rules you can create are:
1) Forward all calls with a given caller-id to my cell phone.
2) If my client calls and I am in a meeting, forward to voicemail.
3) If a call comes, and my Free-Busy status says "Out of office", then call two other numbers configured by me.
I implemented the rules engine for this feature. You can get more details about the feature from the technet page documentation on this feature.