This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
I'm not sure what you mean by "commercial use". The JVM is inherently multi-threaded - where there's a JVM, there are multiple threads.
Servlet containers and JEE servers are multi-threaded with respect to handling simultaneous requests, so wherever there is a web site based on servlets/JSP (or using EJBs in the background), multi-threading is going on. Look for URLs like "*.jsp", *.do" and "...servlet..." - those generally indicate that a site runs on Java.
Even before you start a thread with thread.start() there is a thread for running main(). Also the Java Runtime will have created other threads, such as garbage collection thread. So threads are ubiquitous.