This will allows you to open multiple Roblox windows

ManyRoblox.cpp

#include <windows.h>

int main()
{
    /*
    * OPEN THIS BEFORE ROBLOX
    * DO NOT CLOSE THIS OTHERWISE IT WILL CLOSE ALL ROBLOX PROCESSES EXCEPT ONE
    */
    CreateMutexA(NULL, TRUE, "ROBLOX_singletonMutex");
    while (true);
    return 0;
}