Lazarus is a cross-platform IDE for the Free Pascal compiler. It tries to offer a Delphi-like programming experience through its own 'Lazarus Component Library' and supporting many platforms like Windows, OSX, Linux, BSD, Android, iOS and more.
Free Pascal is a GPL'ed compiler that runs on Linux, Win32, OS/2, 68K and more. Free Pascal is designed to be able to understand and compile Delphi syntax, which is of course OOP. Lazarus is the part of the missing puzzle that will allow you to develop Delphi like programs in all of the above platforms. Unlike Java which strives to be a write once run anywhere, Lazarus and Free Pascal strives for write once compile anywhere. Since the exact same compiler is available on all of the above platforms it means you don't need to do any recoding to produce identical products for different platforms.
Lazarus is completely API independent. Programs could be compiled against Win32, GTK2, Qt, Carbon, FpGUI and more custom drawn widgetsets. With GTK2 and Qt for Windows supported as well.
LCL is largely resembles VCL, so Delphi code could be largely reused.