ArcGIS Online is a cloud-based, collaborative content management system for maps, apps, data, and other geographic information. You can access ArcGIS Online through a web site (www.ArcGIS.com), mobile devices, and desktop map viewers to accomplish the following:
- Create web maps
- Web-enable your data
- Share your maps, data, and apps
- Find relevant and useful basemaps, data, and configurable GIS resources
- Manage content and people in your organization
Portal for ArcGIS provides you with the same core capabilities as ArcGIS Online but can be installed and hosted on your own premises, behind the firewall, for controlled distribution of content. Portal for ArcGIS is the technology that powers ArcGIS Online, available for you to implement in your organization.
ArcGIS Online for organizations, on the other hand, lets your organization be a part of ArcGIS Online through a subscription, without needing to install or manage any server technology. With this subscription you can set up a configurable, secure site that includes administrative controls, flexible data storage capabilities, and other provisions that enable geospatial information to be more pervasive within your organization or to the general public. Through the subscription, you can also access Esri's cloud to turn your data into web-accessible maps.
ArcGIS Runtime SDK for iOS allows developers to access and search content, users, and groups of a general portal (through either an on-premise instance or ArcGIS Online) or a specific organization's subscription within that portal. The SDK uses the ArcGIS Portal REST API to communicate with the back-end portal.