>Providing work to the government without the government paying for it is illegal.
The Anti-Deficiency Act only prohibits "voluntary" services, not "gratuitous" services. Prior to the passage of the law, it was not unusual for cash-strapped gov't agencies to accept "voluntary" services (i.e., no formal obligation to pay for them) but then pay for them later after being allocated more funds. Congress didn't like this so it outlawed the practice. However, if someone wants to donate services to the gov't and executes a written agreement to not accept payment, then it is legal for the government to accept the free services. See, e.g., https://www.gao.gov/assets/450/441639.pdf
Thanks for the important clarification. I think the relevant part for this conversation is that the work still has to be outlined within a contract, and that contract has to specify that there is no compensation. That's a drastically different scenario than pretty much any developer in a government contract situation would find themselves. It would still be illegal to do work outside of that specified in the contract!
The Anti-Deficiency Act only prohibits "voluntary" services, not "gratuitous" services. Prior to the passage of the law, it was not unusual for cash-strapped gov't agencies to accept "voluntary" services (i.e., no formal obligation to pay for them) but then pay for them later after being allocated more funds. Congress didn't like this so it outlawed the practice. However, if someone wants to donate services to the gov't and executes a written agreement to not accept payment, then it is legal for the government to accept the free services. See, e.g., https://www.gao.gov/assets/450/441639.pdf