Especially since, under California law, what you do with your personal time on personal hardware is yours, regardless of employment contract.
https://www.sacattorneys.com/san-jose-intellectual-property-...
The relevant quote is: "It is legal to require an employee to assign intellectual property created in the employee’s own time if it required any of the employer’s tools, facilities, or intellectual property, or if that intellectual property relates to the employer’s business or research and development."
Since Apple operates in a wide swath of the IT world, it is very likely that most OSS developed by Apple employees could reasonably be considered "relate[d] to the employer's business". That is certainly the position that Apple takes in most case (source: I am a former Apple employee).
"(a) Any provision in an employment agreement which provides that an employee shall assign, or offer to assign, any of his or her rights in an invention to his or her employer shall not apply to an invention that the employee developed entirely on his or her own time without using the employer’s equipment, supplies, facilities, or trade secret information except for those inventions that either:
(1) Relate at the time of conception or reduction to practice of the invention to the employer’s business, or actual or demonstrably anticipated research or development of the employer; or
(2) Result from any work performed by the employee for the employer.
(b) To the extent a provision in an employment agreement purports to require an employee to assign an invention otherwise excluded from being required to be assigned under subdivision (a), the provision is against the public policy of this state and is unenforceable."
This is the catch-all and I've always been curious what the seminal cases are which apply this language. For example, the charter for most corporations these days usually establishes the business for "any lawful activity", so if the scope of an employer's business is defined by the charter, then pretty much any commercially viable FOSS project could potentially be ensnared by an employer. Any IP lawyers here have some pointers to how "employer's business" is supposed to be interpreted and applied?
I lost but learned a valuable lesson, one just never knows with the law. These things are where one starts argument, it’s not where they stop.
Lawyers will have to decide how comfortable they are with the risk, and balance it against the reward. It’s totally natural that different entities will come to different conclusions in this environment.