Good question! It was a small niche business called "Computer For Tracts" which leased a complete turnkey solution to new home construction sales offices. You'd find these in new growth areas where home builders have bought a large land parcel to create a new development by building a couple hundred suburban homes (as well as the local streets, parks, etc). Basically, they'd first clear the land and complete four or five homes to show as models of each floor plan. They'd usually turn the garage of one of the models into an onsite sales office which would be staffed by an employee realtor who could discuss all the various options (flooring, paint), lot selection and write up a sales contract. These little makeshift sales offices would operate for 3 or 4 years until the development was sold out, at which time the models would be converted into the last homes sold and the builder would start a new development elsewhere.

The company was started in the early 80s in Southern California by a realtor who'd spent his career in new construction residential sales and knew the biz inside out. New construction residential sales has distinct needs different from residential resales. So he wrote a software program in the ROM BASIC of a Radio Shack Color Computer to do exactly what a new construction sales person needs to do. This involves calculating the financing options including the down payment, monthly payments, taxes and insurance for all the various loan options available, like 30-yr fixed, 15-yr adjustable rate and then sending prospective buyers home with a customized printout showing their options based on their particulars including down payment, rate, credit score, etc.

It was really quite complex under the hood, yet it made all this easy for a sales agent to present clearly to even novice home buyers. It turns out that doing this is well is key to selling the builder's growing inventory of homes and, obviously, there's a lot of money tied up in such a development. His early versions of the program loaded from an external audio cassette tape player by having the user manually press Play, Stop and Rewind. But this was a major problem because new home construction companies aren't IT savvy and the vast majority of realtors (especially in the early 1980s) had never even seen a computer in person before. So, he learned how to burn his custom BASIC program on EPROMs he installed into blank game cartridges inserted into the Color Computer's game cartridge port.

He was then able to offer a self-booting system that his novice users could learn to operate. He marketed it as a complete solution on a monthly lease (including computer, software cartridge, monitor, printer, cables, installation, training, service and support). Since these Radio Shack computers where just a few hundred dollars and his system was extremely valuable to such construction companies, his little garage business grew like wildfire. I think I was the third non-family employee and we were still working out of the garage and back bedrooms of his house before later moving to an office. Eventually, the software became so complex that it wouldn't fit in a ROM cartridge any more, even after I wrote a pretty neat assembly language hack that lived in the game cartridge ROM and took control on every boot to add new commands to the computer's built-in BASIC interpreter before returning control back to the BASIC program. These new BASIC commands allowed programs to swap between four and eventually eight banks each containing an 8K segment of BASIC code and even pass control to a specific BASIC line number in another bank of EPROM-based BASIC code. It was quite a deep hack into the undocumented system but it worked perfectly and is a testament to the benefits of having an all-hardware system where nothing ever persists between boots. When the capabilities of the program eventually expanded so it couldn't fit in 64K or even 128K of dedicated EPROM (in addition to the computer's 64K of RAM), even with lots of very clever byte-counting optimization and compression tricks, we started looking to move off the 8-bit Radio Shack Color Computer to a 16-bit platform with more memory and disk storage - and I started suggesting the just announced (but not yet shipping) Amiga 500 would be ideal (which it was)!

Over the early years of constant iteration and daily customer feedback, the program had evolved to become really perfect for doing this one, extremely valuable yet highly specialized thing and the little company grew fast and was highly profitable. He could charge quite a bit for the monthly lease because no salesperson who'd used it ever wanted to sell without it. It was really that good. In fact, the lease required the first two and last two months payments up front, and this was enough to basically pay for the computer, monitor, printer, power strip, etc. So after that, the rest of the lease contract was all profit (although, service, support and ongoing training had to be available 10 hours a day, seven days a week, including weekend onsite system replacement if necessary (which could involve driving over four or five hours round-trip on a Sunday if you were on-call that weekend)) so the customers definitely got value for their money. And supporting this highly specialized, extremely deep application took at least a full year for a new person to learn (if they were sharp) which is why in the early days we three software coders were also the support, training and field service staff). While strange in today's world, that's probably why this software became so damn polished to perfection for this use case.

For example, after selecting a home model, to update the main financing screen showing all the different loan options, all the agent had to do was punch a different interest rate, monthly payment, or down payment on the 10-key and it would recalculate all the loans with the new parameter. They didn't even have to select an input field because the program dynamically figured out based on the value typed and the sales price if the entered value should be interpreted as a rate, monthly payment or down payment.

In an era before spreadsheets, without this program, it took these agents at least three minutes to change one parameter for one loan on a manual TI paper-tape adding machine. But our program recalced a dozen loans in two seconds (including every possible option from full amortization tables to rate buy-downs). This made providing full, clear and detailed answers to every customer question trivial (like "How much more do I need to put down to reduce the monthly payment by $500?"). To these sales people this seemed like literal voodoo magic ("How does it know that what I typed in was the desired monthly payment?") :-)

Last I heard the company had transitioned the program to Windows PCs sometime in the mid-90s and was still around in some form post-2000.