Russ Nelson <firstname.lastname@example.org> says “I looked into [tax-deductable code donations] in my role as the executive director of the Public Software Fund. If you own copyright on a work, and you donate that work to a 501(c)(3) [non-profit organization], you can deduct the fair market value of that work [from your US taxes].”
Notable relevant organizations include the FreeBSD Foundation, the Apache Software Foundation, and the Free Software Foundation. They must be projects that will formally take ownership of the copyright from the donor.
Russ continues: “The difficulty here is that you need to determine the fair market value. […] So what would a contribution to an existing open source project be worth? […] It seems to me arguable that you can deduct whatever you could sell the first copy for. When Cygnus Software was an independent company, they would sell the first copy of a gcc port for six or seven figures. A comparable price would be the price of full ownership of any comparable piece of software. A less reliable valuation would be the salary of someone paid to do a comparable work-for-hire.”