Lazarus is the best IDE to develope professional Free Pascal applications. It is cross plateform, you can write your applications in your favorate OS like Linux, Windows or Mac, and then recompile your source application on targe operating system to generate native executable for specific plateforms.
Lazarus is a free and open source IDE.
Lazarus official site is:
http://lazarus.freepascal.org/
Lazarus IDE screenshot:
Free Pascal Answers 