While I described production ready SAP Fiori Style Application Architecture Options earlier, this blog is about a light footprint option for SAP Fiori style applications using SAPUI5 on top of SAP Gateway that is suitable for non-productive scenarios e.g. for PoCs.
As you can see from the diagram, this option does not require a local SAP Gateway installation but uses Gateway as a Service (GWaaS) instead, which is available via the SAP HANA Cloud Platform. Since GWaaS is still in beta state, this option is only suitable for non-productive scenarios in the moment. Also you would have to model, develop and register your SAP Gateway services directly on the backends but would not be limited in their number. However you would need a SAP HANA Cloud Connector to connect your backend systems to the SAP HANA Cloud. I also described how to Securely expose SAP NetWeaver Application Server ABAP Services through Gateway as a Service via the SAP HANA Cloud Connector for those interested in the details.