There are a lot of specialty niches in mainstream just like adult as well...
one I'm pursuing with a partner is
http://www.loadbase.com
it's not quite complete yet, but very close.
There are an over 10,000 trucking companies and owner/operators and over 3500 registered freight brokers and they are 5-10 years behind on techonology and eager to learn (when motivated by money ;-))