ACT! - why so many?

I have tried to find and read specs and can’t find th difference between all these.

Why are there so many companies selling ACT! and why do the prices vary so much? Does anyone here know or can they explain the difference between all these. I’m trying to help advise my friend on buying one of these for a small company he is part of but for once I am baffled. They all seem the same but there just must be a difference because some are so expensive and some are so cheap… I doubt it’s such a vast price difference due to one or two being OEM.

durr, i forgot to incl some links of different ones that I found