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Licenses
The core parts of FoGSiEm are dual-licensed under either the terms of the Eclipse Public License v1.0 as published by the Eclipse Foundation (see http://www.eclipse.org/legal/epl-v10.html or license.EPL.txt file in such bundles) or (per the licensee's choosing) under the terms of the GNU General Public License version 2 as published by the Free Software Foundation (see http://www.gnu.org/licenses/gpl-2.0.txt or license.GPL2.txt file in such bundles.
The Eclipse RCP-dependend parts are licensed under the the terms of the Eclipse Public License v1.0 as published by the Eclipse Foundation (see http://www.eclipse.org/legal/epl-v10.html or license.EPL.txt file in such bundles).
For details, please check the about.html in each plug-in.
Because the GPL and EPL are not compatible. Although there had not been any court proceedings about this issue, the Eclipse Foundation (post by Mike Milinkovich) as well as the Free Software Foundation (post by Brett Smith) state that EPL and GPL are not compatible. Since the video-related parts depend on GPL software (which do not include Eclipse in their exception statement), we decided to split both parts.
Although all plug-ins can be combined technically, this licensing issue prevents the release of a single application with all plug-ins. Thus, the main release of FoGSiEm contains only a subset of plug-ins and is licensed under the terms of the EPL. It would be possible to release a video-centric set under the GPL 2.0 for GPL-OSGi implementations (e.g. Glassfish).
The main problem arises from the video-related parts. The video-related parts of FoGSiEm are relying on libraries, which are available under the GPL 2.0. Thus, the parts linking against such libraries have to be licensed under the GPL as well. Consequently, the video-related plug-ins are made available under the GPL 2.0. The problem arises by combining these plug-ins with plug-ins depending on the Rich Client Platform (RCP). From the GPL point of view, the GPL is "transitive" meaning that all parts linked with a GPL part have to be GPL. That even applies to plug-in frameworks, which combines plug-ins at runtime. Thus, the RCP parts would have to be licensed under the GPL. However, they are released by the Eclipse Foundation under the conditions of the EPL. Although there was no court proceedings about this issue, the Eclipse Foundation as well as the Free Software Foundation state that EPL and GPL are not compatible (cp. links in previous section). The solution for this problem is a split of the plug-ins in two "applications". One application contains the video-related plug-ins while another application contains the remaining plug-ins. Both can be connected at runtime via inter-process communication. For example, both can setup FoG entities, which are connected by gates accessing lower layers, such as Ethernet and IP. The parts of FoGSiEm required for both applications, e.g., the FoG core simulation, are dual-licensed under the EPL and GPL 2.0. That includes some plug-ins, which re-implement RCP functionality required by the core simulation such as the extension point mechanism. The OSGi dependencies for bundles do not have to be re-implemented since OSGi implementations under the GPL are already available.
The FoGSiEm parts depending on the RCP are licensed with the EPL. The license forces others to make changes at FoGSiEm again open-source under the EPL. Thus, all modified versions of FoGSiEm remains open-source. Since EPL allows dependencies between EPL- and non-EPL-plug-ins, contributors of extensions to FoGSiEm (meaning plug-ins with extensions to the extension points of FoGSiEm) have a variety of choices for their license, such as BSD license, Apache License, and commercial licenses. GPL is only appropriate if it contains an exception clause for FoGSiEm and Eclipse.