BitShares is the decentralized platform, the DEX. OpenLedger is a company built on top of the platform. They run a gateway service that allows users to deposit and withdraw cryptocurrencies. When you deposit they send you an equal amount in their UIA, withdrawal exchanges the UIA for a payment on a different chain. Their UIAs are traded on the DEX. The trading pairs are accessible from any interface, not just OpenLedger's hosted wallet. OpenLedger tokens have counterparty trust, unlike bitAssets and BTS.

Obits are a token issued by OpenLedger. There is a monthly buyback & burn + dividend distribution to holders of obits.