To do this right, you really must consider the type of load you have and what it needs. If it is just an AC 3 phase motor, any VFD can do this. Servo motors likely use a converter to change the AC to DC too, they rarely care about input frequency. If it is any other type of converter, ie power supply, it may not care at all, or it may be very sensitive, which means that inexpensive square wave UPS systems may make it worse. If it is resistive heating, it will not care, but if the heaters are controlled by SCR power controllers, they might. There is just no simplistic answer in the absense of more detail.
"Will work for (the memory of) salami"