FOSDEM (Free and Open Source Software Developers' European Meeting) is the largest European FOSS conference — free to attend, volunteer-organized, and held annually at the Université libre de Bruxelles — and one of the movement's defining community institutions.
FOSDEM was started in 2000 by Raphael Bauduin under the name OSDEM (Open Source Developers' European Meeting). richard-stallman objected to the name because "open source" excluded the "free software" tradition; Bauduin renamed it FOSDEM — incorporating both "free" and "open source" — at Stallman's request. This naming negotiation is itself a small case study in the politics of software-freedom-vs-open-source.
FOSDEM's defining characteristics distinguish it from commercially organized conferences like OSCON (organized by tim-oreilly's company):
Free admission: FOSDEM charges no registration fee. Funding comes from sponsorships and merchandise. This makes it accessible to contributors who cannot afford expensive conference registrations — a significant portion of the volunteer FOSS community.
Volunteer organization: FOSDEM is organized entirely by volunteers, with no professional conference staff. The organizing committee is small and the infrastructure is maintained by the community.
Developer rooms: FOSDEM's format includes dozens of "developer rooms" — half-day or full-day tracks organized by specific projects and communities (the Mozilla room, the PostgreSQL room, the kernel room). These function as project community gatherings embedded within a larger conference, enabling both technical sessions and face-to-face collaboration among distributed volunteer teams.
Scale: FOSDEM regularly attracts 8,000+ attendees across two days in February, making it one of the largest annual FOSS gatherings in the world despite (or because of) its non-commercial structure.
FOSDEM has remained consistent through the mainstream-adoption-and-corporate-embrace-2005-2014 and modern-foss-and-sustainability-crisis-2015-present eras — a stable point of annual community gathering that predates github-platform and continues alongside it, maintaining the face-to-face community dimension of the movement that online platforms cannot fully replace.