That really depends on what type of software you're referring to and in what industry. Generally speaking, the software with the most sales will be products geared towards consumer use, like computer operating systems, media players, and security software. Businesses tend to spend more on enterprise software like database management software, customer relationship management software, and analytics software. Popular services like Microsoft Office and SaaS solutions are also big money-makers. Ultimately, the software that sells the most is whichever product can provide the best value and the most convenience to its users.