These days porting from one platform to another in Pascal or Object Pascal is becoming much more accessible. Not only can this all be done with the FPC and Lazarus projects, but very soon Embarcadero is going to be releasing new versions of Delphi that will support both Mac OS X and Linux. If you don't mind managed code, you can also port it to .NET and with Mono support you can create managed code ports on these systems this way as well.

However if you prefer native executable solutions Free Pascal and Lazarus are the way to go until the new ports of Delphi come out.