Details of ThreadCount  property as described in the BW 6.2.0 documentation. 

"The rate at which the BusinessWorks engine can execute and complete processes depends on the ThreadCount and StepCount engine properties. ThreadCount (bw.engine.threadCount): The process instances in memory are executed by the engine. The number of process instances that can be executed concurrently by the engine is limited by the maximum number of threads specified by the ThreadCount property. By default, the thread count is eight. Threads execute a finite number of tasks or activities uninterrupted and then yield to the next process instance that is ready. The CPU and memory resources should be measured under a typical processing load to determine if the default ThreadCount is suitable for your environment."

However, this does not explain how the ThreadCount property works at the application level. The threadcount property is defined for the appnode itself and the appnode is a single JVM which can run multiple applications. All applications running in the appnode will share the number of threads specified by the threadcount property for that specific appnode. As an example, if the threadcount for an appnode is defined as eight and three applications are running in that appnode, the eight threads will be shared by all three applications.