Lazarus For Delphi Users/de
Delphi -> Lazarus
Lazarus is an Rapid Application Development (RAD) tool like Delphi. That means it comes with a visual component library and an IDE. The lazarus component library (LCL) is very similar to Delphi's VCL. Most units, classes and properties have the same name and functionality. This makes porting easy. But Lazarus is *not* an 'open source Delphi clone'. So don't expect 100% compatibility.
The biggest differences
Lazarus is completely open source, is written platform independent and uses the mighty Free Pascal compiler (FPC). FPC runs on more than 15 platforms. But not all packages and libs are ported, so Lazarus currently runs on Linux, Free/Open/NetBSD, and the MacOSX and win32 port is under heavy development.
Lazarus is not complete, as is this text. We are always searching for new developers, packagers, porters, documentation writers, ... .