Yes and no is probably the right answer
The original Testbook was a sexy custom built thing, hinged touch-screen, with all the kit inside the computer and you just plugged in some cables and off you went. Not sure what Testbook 2 and Testbook 3 were.
As is the way of things (I think they call it progress ) the T4 is now a standard Dell laptop bolted onto a box of junk which does the serial interfacey twiddly things (as you can tell I am an IT boffin....). Which is also apparently why it is called the T4 because I believe that Hewlett Packard (who built the original Testbook for Land Rover) own the "Testbook" trademark. Presumably they were less than impressed at not being asked to build the replacement and told LR to bog off when they asked to transfer the name!
So yes I think you could install the software on a standard laptop, but I suspect it would be F all use if you didn't have the (very expensive) bit that sits underneath the laptop and talks to the laptop through one orifice and the vehicle through another plus of course all the different leads (of which there are several).
I have not seen a Rovacom but I think their software is totally different and my understanding is that it also requires a bit of hardware (some sort of serial interface box thing), just that it is a lot less expensive than the Land Rover offering! I did look into it with the intention of getting the required bits to do my Discovery a year or so back but decided that as the Disco wasn't broken I couldn't be bothered..... the different bits required to do all the vehicle systems added up to a grand or so ISTR.
I think a T4 was running at about eight or nine grand a couple of years ago, anybody can buy them now, same as all the technical info is available online at www.landrovertechinfo.com you just need a credit card. One of the few useful things the EU has done is to open up access to all this stuff... but you still need £££££££££!