Free Pascal is an open-source compiler for the Pascal and Object Pascal languages, and it's not tied to any specific development environment. Delphi, on the other hand, is an integrated development environment (IDE) that uses the Object Pascal language. While Delphi is a commercial product by Embarcadero Technologies, Free Pascal is a free and open-source alternative. However, they share a common language base, and code written in one can often be used in the other.