Which aspect of what types of computer software. There are well over 1000 different softprorams to test various... each cpu socket series, each motherboard series, and so on requires different test procedures. There are, for instance, 87 different programs I know of which deal with the registry. You will not find a grab bag of test software. You will have good luck by doing a google search by problem area, then you need to have experience in using each package to find what is good. Once you know the software, you can search for opinons on the various forums or with the many search engines.
We have been in the computer repair service since the WANG computers of 1975, and the MITS in personal computers. We would have been delighted to know good software.
We have in our shop a variety of test software just for the Sony VAIO. We have over 200 discs to cover all the Compaq Presario models and problems.
So if you will list specifics of the problems with which you wish to begin, we can perhaps offer suggestions. But we need details. Specifics.
First, I recommend a good book, like old versions 1995, 2000, and 2006 versions of Scott Meullar's Rebuilding and Repairing Personal computers. Start with computers you know then add to that knowledge with these books. The best tool will be your memory.
For software, I would begin with a problem, then add to your knowledge with the tools you find in the software sold or free on www.tucows.com, www.majorgeeks.com, www.pcworld.com, www.cnet.com, www.pcmag.com and sites such as this one you now visit.
On top of this, every technician seems to have their own favorites.
If I were to start in one area, it would be in saving and transferring files, address books, and the likes, for which there are easily 50 different packages. For hardware, I would start with test hardware and related hardware for Power supplies.
By requent failure areas, we find the problems are greatest in these areas, highest first: Floppy drives, Speakers, DVD burners, CD burners, power supplies, Power switches, CMOS batteries, Windows ME errors, Windows 95 errors, Windows 98, W2k, then WXP, Memory modules, video cards, modems, CPU Fans, USB boards, NIC, CPU, Motherboards... the list never ends.
If you are expert in one area, add to it with software, or pick a second area.
We have people in our shop who only work on Sony VAIO because they are the most problematic. Second is Packard Bell and Aer. Currently the main subspecialty is an eMachine WXP desktop. There is no software for any of those that helps much.
When you know enough information and have enough experience to know what software to ask for, you are getting some place.