Using threads in Java, you can create an applet so that it runs in its own thread, and it will happily run all by itself without interfering with any other part of the system. Using threads, you can have lots of applets running at once on the same page. Depending on how many you have, you may eventually exhaust the system so that all of them will run slower, but all of them will run independently.
JAVA API reference :
Northest Parallel Architectures Center, Syracuse University.