The Dash Platform provides a technology stack on the top of Dash Network that allows creation of feature-rich decentralized applications.
You can learn more from the Dash Platform Documentation - What is Dash Platform?
DAPI: A decentralized API that runs on all Masternodes and offers gRPC endpoints for retrieving payment chain metadata (blocks, transactions), as well as application data (documents, contracts, identities).
Drive: Application chain storage layer where the data defined by Data Contracts is stored and managed.
DPNS: Naming service provided by a Dash Platform App