Application Platform as a Service - aPaaS | WaveMaker
"...services that primarily offer application development and deployment are referred to as application Platform as a Service or aPaaS while PaaS refers to entire spectrum of middleware as a service offerings..."
Market Guide for Application Platforms @ Gartner
"Commercial Java Platform, Enterprise Edition (Java EE) platforms' revenue declined in 2015, indicating a clear shift in the application platform market.
Application platform as a service (aPaaS) revenue is currently less than half of application platform software revenue, but aPaaS is growing at an annual rate of 18.5%, and aPaaS sales will supersede platform software sales by 2023."
SalesForce is more than 50% of SaaS market now, and Microsoft is growing quickly Office 365. They both support "Apps" and marketplaces / stores for those apps.