"On this day long ago, a child was born who, by age 30, would transform the world. Happy Birthday Isaac Newton b. Dec. 25, 1642."
-- Neil deGrasse Tyson, Twitter, December 5, 2014
Newtonmas is an atheist/geek repurposing of Christmas, in which one celebrates all things science during an internationally recognized schelling point. It has been around on the internet since at least 2007, and the true origins are lost in time. Traditions vary greatly, but Newtonmas celebrations tend to have a few common factors.
1. Science: giving technological gifts, doing interesting experiments, or just giving thanks that we no longer live in the squalor of 1642 England (Thanks, Science!).
2. Apples: We eat them. Do not drop on people's head, that only worked once.
3. Annoying Traditionalists: Sometimes on purpose, sometimes accidentally. There's a very serious don't-mess-with-Christmas crowd out there, and they will be hating.
Everything else is pretty much optional... common variants involve a hard-line stance against celebrating mythological beings, their slave elves and reindeer, and other trappings of religions tradition; an easygoing stance accepting all holiday traditions into Newtonmas in a spirit of open-mindedness and community; and the extension of Newtonmas for the entire ten days between December 25 to January 4, thus including both Newton's original birth date under the Julian calendar through his new, improved birthday under the Gregorian calendar.
Of course, the true spirit of invention is to make up your own traditions. There are all too few celebrations of calculus and optics; go get celebrating!