hackfest
Any event centered around programming and the rapid development of code over many consecutive hours, sometimes days. Hackfests are akin to LAN parties, all-nighters, weekend benders, etc, but deal specifically with programming. Some hackfests have themes involving specific programming languages, projects, or locations.
Agbar won't be able to make it to your birthday party, he's at a hackfest and they're not leaving until they develop a program to measure the number of bleeps in an episode of South Park.