While Segment is not, itself, an analytics tool, it's basically a funnel through which you can push all your analytics events, which it will then send out to all the services you use that rely on event data.

For example, with Segment you can easily integrate Mixpanel, Google Analytics, AutoPilot, Heap, Mailchimp, Olark, Zendesk, and more.

You can also send all your data, from various sources, to your own data warehouse for analysis.