Substrate & Ink
To interact with Polkadot, there are three envisioned development trajectories; a parachain implements it’s own runtime logic (think custom sidechain), a parathread is similar but only produces a block when absolutely necessary to update the relay chain, and a smart contract can run atop any chain with the correct execution environment. Substrate enables the former methodology based on a modular architecture with pluggable consensus and Parity maintain an embedded Domain Specific Language (eDSL) atop Substrate for WASM smart contracts.