OpenRA

Is it legal to make your own game using the OpenRA engine and release it commercially?

Yes it is. But since it's released under GPL, so you have to provide your modified source then.

https://github.com/TM-PD/FirstDance (was a private github repo in the past) is an example of a (failed) commercial clone which was used in a strange in-house software as a service project to "educate" children. They probably underestimated the effort it takes to maintain such a huge project and abandoned it after some months of mostly re-branding. Sadly they never sent a single patch back to where they forked from and only released the source code after I found out when reading about OpenRA in some developer biographys on linkedin.com I had never heard of. Note: that was mostly illegal. Don't do that even if your boss fears competition. Otherwise risk getting in trouble with http://gpl-violations.org/

Conclusion: my tip is to work with us, try to include your patches into the main OpenRA distribution and use it as a basis for your mod/content. http://www.desura.com/games/publish/openra/settings might need some tweaks to allow selling DLCs. Another legal advice: it has to be a total conversion. If you earn money with trademarks and EULA covered content, the lawyers at Electronic Arts might send you angry letters.

Interesting topic.

Cmd. Matt wrote: ↑If you earn money with trademarks and EULA covered content, the lawyers at Electronic Arts might send you angry letters.

Out of curiosity, does that include WW's own file formats like shp, tmp, aud and so on?
In other words, would a commercial project have to implement non-proprietary alternatives to them?

That is an interesting question. In Germany reverse engineering is legal to make your own product compatible to a competitor. These are exceptions to patent and copyright laws to prevent market failure. I don't know the situation world-wide. Plus we don't do checks if we violate software patents or similiar IP rights for every patch we recieve. This is not a corporate conducted Open Source project, but a hobbyist initiative. But I don't know of any Free Software RTS engine project that is tailored towards business friendliness. The weird Westwood file formats definitely complicate things for artists that are not used to them.