Platform as a service
Platform as a service (PaaS) is a category of cloud computing services that provides a computing platform and a solution stack as a service. Along with software as a service (SaaS) and infrastructure as a service (IaaS), it is a service model of cloud computing. In this model, the consumer creates an application or service using tools and/or libraries from the provider. The consumer also controls software deployment and configuration settings. The provider provides the networks, servers, storage, and other services that are required to host the consumer's application.
PaaS offerings facilitate the deployment of applications or services without the cost and complexity of buying and managing the underlying hardware and software and provisioning hosting capabilities. All "as-a-service" offerings are characterized as providing low initial cost, incremental cost as your service usage grows, self-service, best practices built-in, resource sharing, automated deployment, management services, lifecycle management, reuse. PaaS provides these capabilities for application and service development.
There are various types of PaaS vendors; however, all offer application hosting and a deployment environment, along with various integrated services. Services offer varying levels of scalability and maintenance.
PaaS offerings may also include facilities for application design, application development, testing, and deployment as well as services such as team collaboration, web service integration, and marshalling, database integration, security, scalability, storage, persistence, state management, application versioning, application instrumentation, and developer community facilitation.
There are a number of reasons why PaaS is experiencing fast market adoption. Today, there are compelling economics around these offerings. Not only does PaaS allow IT teams to do much more with what they have; it also reduces development time - in some instances by as much as 50 percent. Add to this the fact that the market is now maturing and you can start to see why organizations are seeking out PaaS options. 
- Add-on development facilities
- These facilities customization of existing software-as-a-service (SaaS) applications, and in some ways are the equivalent of macro language customization facilities provided with packaged software applications such as Lotus Notes, or Microsoft Word. Often these require PaaS developers and their users to purchase subscriptions to the co-resident SaaS application.
- Stand alone development environments
- Stand-alone PaaS environments do not include technical, licensing or financial dependencies on specific SaaS applications or web services, and are intended to provide a generalized development environment.
- Application delivery-only environments
- Delivery-only PaaS offerings do not include development, debugging and test capabilities as part of the service, though they may be supplied offline (via an Eclipse plugin for example). The services provided generally focus on security and on-demand scalability.
- Open platform as a service
- This type of PaaS does not include hosting as such, rather it provides open source software to allow a PaaS provider to run applications. For example, AppScale allows a user to deploy some applications written for Google App Engine to their own servers, providing datastore access from a standard SQL or NoSQL database. Some open platforms let the developer use any programming language, any database, any operating system, any server, etc. to deploy their applications.
- Mobile PaaS (mPaaS)
- The Yankee Group recently identified mobile PaaS (mPaas) as one of its themes for 2014, naming a number of providers including Kinvey, AnyPresence, FeedHenry, FatFractal and Point.io. 
||This section contains embedded lists that may be poorly defined, unverified or indiscriminate. (June 2014)|
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