The Stellar network is a distributed blockchain based ledger and database that facilitates cross-asset transfers of value, including payments. The native digital asset of Stellar is called Lumens (XLM).
Stellar.org, the organization that supports Stellar, is centralized like Ripple and meant to handle cross platform transactions and micro transactions like Ripple. However, unlike Ripple, Stellar.org is non-profit and their platform itself is open source and decentralized.
Most applications interact with the Stellar network through Horizon, a RESTful HTTP API server. Horizon gives you a straightforward way to submit transactions, check accounts, and subscribe to events. Because it’s just HTTP, you can communicate with Horizon using your web browser, simple command line tools like cURL, or the Stellar SDK for your favorite programming language.
More info on running SDK's on a Stellar node