Stetic is a GTK#

Gtk Sharp

Gtk# is a set of .NET bindings for the GTK+ GUI toolkit and assorted GNOME libraries. The library facilitates building graphical GNOME applications using Mono or any other compliant CLR...

 GUI designer used in MonoDevelop

MonoDevelop

MonoDevelop is an open source integrated development environment for the Linux platform, Mac OS X, and Microsoft Windows, primarily targeted for the development of software that uses both the Mono and Microsoft .NET frameworks...

 to develop Forms, or windows, to run on the Mono

Mono (software)

Mono, pronounced , is a free and open source project led by Xamarin to create an Ecma standard compliant .NET-compatible set of tools including, among others, a C# compiler and a Common Language Runtime....

 implementation of the Microsoft.NET

.NET Framework

The .NET Framework is a software framework that runs primarily on Microsoft Windows. It includes a large library and supports several programming languages which allows language interoperability...

 framework. It has been included since version 0.1 of Monodevelop. Stetic is very similar to Glade Interface Designer

Glade Interface Designer

Glade Interface Designer is a graphical user interface builder for GTK+, with additional components for GNOME. In its third version, Glade is programming language–independent, and does not produce code for events, but rather an XML file that is then used with an appropriate binding .Glade is...

 but is integrated into Monodevelop with features such as drag and drop. It has been criticized of being more difficult to work with than the likes of QT Designer and the Microsoft Visual Studio Windows Forms Editor when the programmer does not yet have a concrete layout in mind.