Using Gekko means accepting that Gekko is provided as open source under the GNU GPL licence. The full EULA, which is also provided as the file README in the souce code distribution, reads as follows (Gekko 1.6):

      ---------------------------------------------------------
          Gekko Simulation Software (www.t-t.dk/gekko).
          Copyright (C) 2013, Thomas Thomsen, T-T Analyse.
      ---------------------------------------------------------

These files are source code regarding Gekko Simulation Software. The source code
is mostly in C#.NET, and is open source licensed (GNU GPL).

Open the solution file (GekkoCS.sln) with Visual Studio 2008 or later. Make sure that the solution configuration is set to "Debug", and the solution platform is set to "Any CPU". Also make sure that the Gekko project is chosen as "StartUp Project". Next, it should be possible to start the Gekko application under Visual Studio by simply pressing F5.

Please note that the software is open source (GNU GPL). That is, it is free of charge, but the source code cannot be used in commercial applications. The source code can only be used and modified in other open source projects. See the GNU GPL licence in the file COPYING, or at http://www.gnu.org/licenses.

Much more information about Gekko can be found at www.t-t.dk/gekko.

Good luck with using the source code. Improvements, bug fixes, suggestions etc. can be sent to the mail address shown at www.t-t.dk.

  Thomas Thomsen/T-T Analyse, editor of the Gekko project (see www.t-t.dk/gekko/fundats.html).