How far I can go in order to open source the project which is based on closed/commercial project where the whole source code (assuming the access is there) has been converted into different state or programming language (either manually or automatically by transcompiling)? So for example no single line (or resource) matches the original one, then who would notice that it was transcoded?

Under what (if any) circumstances can such a project be released with an open source license?

Few simple examples: OpenRA, OpenTomb, OpenTibia, however I'm not sure how relevant they are, as they're complete remakes.

2 Answers 2


You can't do that.

When you adapt the work, you are creating a derivative work you have no license to distribute for. You can't re-license and distribute this work under any license as you don't own the full copyright.

People noticing you break the licensing terms of a product doesn't have any influence on whether you are allowed to break the licensing terms. You are not allowed to do this regardless of anyone noticing.

With regard to the examples, these are remakes; they take the underlying idea of the games, and re-implement it from scratch. This usually doesn't create a derivative work, though care must be taken other intellectual property laws (specifically trademark law) aren't violated.


Martijn is right: you can't transcompile, translate, transliterate, or in any other way transcribe and distribute the code of a work you don't have the rights to do so for. In most commercial proprietary ventures, you don't have those rights, so you can't do this.

However, you can attempt to recreate the software. Many people do this: there are open source clones of Photoshop, of many popular games, of Stack Exchange, around on the internet. This is possible because you're not reusing their code, you're writing your own code to come up with a similar result. Just be careful not to use any of their trademarks.

  • 1
    Most ToSes specifically prohibit reverse engineering, decompiling, etc.
    – hBy2Py
    Commented Aug 28, 2015 at 2:33
  • 5
    If you were to attempt to recreate the functions of closed software, I believe (but IANAL) you may be on shaky ground if you have had access to the close software's source, as it would be difficult to prove you've not copied or derived from it.
    – TripeHound
    Commented Aug 28, 2015 at 8:43
  • 1
    @TripeHound for that reason the GNU project insisted in redoing the Unix tools with different objectives, I. e. high performance or extensibility or no limitations. Precisely to have a defense against "copying".
    – vonbrand
    Commented Sep 30, 2015 at 2:50
  • @TripeHound makes a good point, and this is where a Chinese wall comes in handy
    – Tim Malone
    Commented Sep 16, 2016 at 21:57

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