Can a SIMBL plug-in be proprietary and closed source?

Question

I'm not sure, because SIMBL is GPL.

Answer 1

Here's the answer from the official web-page:

1. You can use SIMBL for anything you like.
2. You can include the SIMBL.pkg with your distribution, but you need to include the original license and ReadMe files so people know what they are getting.
3. If you want more from SIMBL, check out the source and make change suggestions. You can modify the code, but if you release it, you must release the source code as well. On a more general note, please do not distribute a modified version of the code under the SIMBL name -- it would make my life a nightmare. If we can't work your changes into the real SIMBL, give it another fairly different sounding name!
4. There is no warranty of any kind.
5. If you are using SIMBL in a commercial product, please make a donation to support this project.

Answer 2

1. Are you linking with any SIMBL libraries or including SIMBL header files? If so, then you would need to have a GPL compatible license for your code.
2. Are you modifying SIMBL in any way? If so, you would need to release your changes to SIMBL.

If either of those conditions don't apply, then you are safe from the GPL.

Disclaimer: I am not a lawyer. This is not legal advice.