There was a time when the leaders of software-as-a-service companies had to move their lips slowly when describing their business models to investors. No longer.  

After finally getting comfortable with how their businesses work, investors have flocked to the stocks of SaaS companies—which charge customers subscriptions for their software, rather than hefty upfront licensing fees—while a growing number of mature, well-funded companies are filing to go public. In the latest sign of investor enthusiasm for the sector, Zoom, a provider of a video conferencing service, raised the offering price for its shares on Tuesday and is expected to begin trading this week. The Information compiled a list of six companies that have embraced the SaaS model and are expected to stage their own IPOs in the next year or so.