Near Field Communications is fun. And sometimes even useful. The idea is that you bring your phone close to an NFC tag which contains an antenna and a tiny chip which can store data. The phone reads the data and does something. You can program an NFC tag to trigger one of a variety of different actions, from opening a web page, running a program to sending an email.
The Nokia NFC Writer program makes it very easy to program tags. I’ve got a tag in the car that starts the phone playing music. I could also use a tag to configure the phone and even send tweets, as James has done.
There are lots of styles and designs of tags out there. I got the Task Launcher Pack from rapidnfc.com above which provides a lot of fun for around 12 pounds. You can get custom printed tags and people like Moo are even planning business cards with tags in.
There is an API that you can use to allow your Windows Phone program to read and write tag information which has all kinds of possible applications. You can find out more from MSDN here and from Nokia here.
If you have an NFC capable phone (the Nokia 820 and 920 are) then you should have a go. Great fun.
Nokia NFC: It looks like some folks are having a problem finding this program via the link above. It works fine in the UK, I'm not sure what regions of the world have access to it. If the link doesn't work try searching your Marketplace for "nfc".