Gecko (software), the open source web browser layout engine used in many applications developed by the Mozilla Foundation (notably Firefox and Thunderbird), as well as in many other open source software projects.
GeckOS, an experimental operating system for MOS 6502 and compatible processors
Militaryedit
SA-8 Gecko, the NATO reporting name for the Russian Antey 9K33 "Osa", a mobile short-range tactical surface-to-air missile system
Objective Gecko, part of the October 7 – December 17, 2001 United States invasion of Afghanistan