All my work is licensed under GPL (v2 upwards) which includes the following terms:

1. You are allowed to use the unmodified NewGRFs for your needs as you like. (commercial and whatever...)
2. You are allowed to use the source and modify it as long as your work will go back to the community. With following points.
   1. free and opensource
   2. credits also for co-authors

Copyright (C) 2009 Marcel "Ammler" Gmür (newgrf-license@ammler.ch)

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110, USA