Hello,
There is no hard limit to the number of HyperSizer applications that can be run on a PC - it would just be based on available computer resources. The primary limitation to be aware of is that it is inadvisable to work in the same database file through multiple instances of the software. This could potentially cause corruption or errors.
Working in multiple database files through multiple instances of the application should be perfectly safe and not see notable performance degradation unless you are reaching the limit of your disk, CPU, or memory performance.
Thanks,
Stephen