Salesforce Platform APIs – Biswajeet Samal's Blog

REST API: Access objects in your organization using REST.
SOAP API: Integrate your organization’s data with other applications using SOAP.
Tooling API: Build custom development tools for Force.com applications.
Chatter REST API: Access Chatter feeds and social data such as users, groups, followers, and files using REST.
Bulk API: Load or delete large numbers of records.
Metadata API: Manage customizations in your org and build tools that manage the metadata model (not the data, itself).
Streaming API: Provide a stream of data reflecting data changes in your organization.
Apex REST API: Build your own REST API in Apex. This API exposes Apex classes as RESTful Web services.
Apex SOAP API: Create custom SOAP Web services in Apex. This API exposes Apex classes as SOAP Web services.
Data.com API: Data.com provides 100% complete, high quality data, updated in real-time in the cloud, and with comprehensive coverage worldwide.