Sunday is Father's Day in many parts of the world, and while it's never too late to pick up another tie for good ol' dad (the 8-bit version is always a good choice), I've got a few more open source suggestions for you.
Assuming your dad is the sort who knows what cufflinks are for, the iCufflinks will make him the geekiest open source dad at the ball. An LED pulses softly behind the power symbol.
And although the naming choice may make you skeptical, iCufflinks are indeed open source. The source code, circuit board files, schematics and CAD files are all posted on GitHub, which means that instead of spending Sunday in a hammock, Dad can hack at his new tiny toys. And by Mother's Day next year, you should be able to get Mom the matching necklace!
ISS-Notify, pictured above, lets you know when the international space station is visible overhead. Even if it's daytime, a gentle glow will let you know that several people just passed by some 200 miles over your head.
This is a current Kickstarter project still accepting donations. So since it's getting a bit last minute, and shipping something probably won't help you have a gift on Sunday, how about a donation in Dad's name? For $40, he'll get the circuit board and parts. For $85, he'll get a finished, signed ISS-Notify light.
As a side note, if this is the sort of thing that interests you, you can also follow @twisst40 on Twitter to get messages notifying you when the ISS will pass your location. But that doesn't mean you shouldn't also get a light to remind you.
Finally, if what you really need is something in Dad's hands on Sunday and you still haven't done anything about it, it's time to turn to the procrastinator's friend: overnight shipping.
Several Arduino and related hacking books have come out in just the last few months: