(Source: YourStory.com) Segment-wise, software-as-a-service (SaaS) will continue to be the largest with revenues increasing 22.2 percent to $73.6 billion in 2018. By 2021, it will account for nearly 45 percent of total application software spending with revenues crossing $117 billion, according to Gartner. Sid Nag, Research Director at Gartner, said:.