Can I use just one part, or do I need the whole platform?

You can use the parts you need. social.plus is modular: you can start with chat alone, add feeds or groups and forums later, and expand into monetization or analytics when your product is ready. The documentation includes setup paths for specific use cases like direct messages, group chat and live chat. You can use the UIKit components or build your own interface on the SDKs and APIs. Circle bundles its features by pricing tier, with more capabilities available on higher plans.