In the future, when looking at github becomes a standard hiring practice, companies will start going full closed source so that their talent can’t jump ship.
My former employer, a Fortune 500 company, wouldn't let me volunteer for a globally recognized charity because the boilerplate agreement the charity required volunteers sign, stated that IP created as a volunteer belonged to them, and my employer considered that everything within or outside work hours was theirs. Not that I was volunteering as a programmer anyway.
My current employer doesn't have explicit rules that I'm aware of, but early on, I asked our HR person if I could work on open source outside work and they said something along the lines of "what's open source?" Which, I mean, on the one hand what do you expect from HR, but on the other hand, the entire agency is concerned with operating, maintaining, and developing a software system.
I was under the impression that this kind of interpretation of employment contracts was more or less illegal (or, at the very least, unenforceable) in many states (I'm assuming you're US, programming in Fortune 500, so maybe not applicable?). Sort of fits into the same kind vein as certain non-compete clauses, where companies put them in, but they'd be tossed out pretty quickly in court should things actually reach that point.
If it's not on employer-owned equipment during core working hours, then I believe it's pretty difficult for an employer to enforce that kind of thing. I don't know how important to you working at that charity was or participating in open-source now is to you, but if you're willing to take a harder line of telling rather than asking, you might find that when push comes to shove, there might not be much they can do without drastically escalating the situation (not always an organization's favorite thing to do, even if they can technically win, which they might not be able to).
Obvious disclaimer about being a non-expert on this sort of thing, but really just wanted to point out that the first answer in this situation may not actually be the final one.
My recollection is there was a compulsory agreement saying you would not do anything of a nature related to your work, or if you did, allow the company to decide if they wanted to claim it.
Also, running side businesses was not allowed.
Of course, the normal thing to do was just ignore the rules, because most likely nobody would notice or care. I explicitly asked for permission because I wanted to see what would happen.
This is how I get over that hump. Not only do I not work on anything related to my day job, I mostly build things in my free time that aren't really useful to anyone but myself. Sure my company may be able to claim ownership of my Sean Connery themed programming language but will they? What on earth do they plan to do with it?
They are happy that you can't leave, because you have nothing to legally show to other interviewers and no other prospective project in your drawer. That's not a good position to be in.
I would love to see a push for more intellectual ownership over the code you contribute to your employer. I should be able to take any snippet I wrote and reuse it with impunity.
This might require engineers unionizing, but it would be a boon to the field. Patterns buried in closed source vaults would be disseminated and innovation would surge. It might usher in a golden age of software if everyone were able to freely share their intellectual ideas with their peers and not have to worry about risking their health insurance and home in the process.
