ArcGIS Desktop versus Milsoft? What's the Difference?

I apologize if this is posted in the wrong spot- I'm brand new to the ESRI forums and I didn't see anything specifically for general Q&A.

I am a consultant who is helping a client (small city with a population of less than 10,000) get a GIS program implemented. During a meeting, the utility manager mentioned something called Milsoft, which apparently the area power co-op uses. Now, I am pretty familiar with ArcGIS, having worked extensively with version 9.x and 10.1 in grad school, but being fresh out of grad school I have never heard of MilSoft before. I have been reading up on this product but I am still struggling to understand how it relates to/compares to ArcGIS desktop. The Milsoft website is no help- it's a bit too general, I think, to answer my clients' questions and mine.

Does MilSoft do the same things as ArcGIS? Is it an add-on? Is it true GIS? What's the deal, anyway?

I need to know what MilSoft is and does compared to ArcGIS for desktop, and I am hoping that folks who are familiar with these two products can tell me the main differences as far as what they are capable of and are best used for. Any information that can be provided is greatly appreciated.

Thanks!