End mills are similar to the spiral bits that we woodworkers use, only they are designed for use with metal. However they can often be had at lower prices, especially long bits. This recent thread on the Festool Owners Group has some good information on using end mill bits in a router. Post #12 has a lot of information. The catch is that, according to the thread, bits larger than 3/8″ diameter are usually shanked to size (the shank size is equal to the cutter’s diameter) which means that you can’t use bits larger than 1/2″ diameter.
Sculptural Woodwork by Chris Wong 
Great info. Thanks for sharing.
I always wondered if I could use of one of those end mills in my router.