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For some value of significant, Squeak. The turn out has been down for the last few elections, with the last one getting around a hundred votes, with around 450 people authorized to vote.

Some of the decline is probably linked to the Pharo fork http://www.pharo-project.org/home

The FreeBSD Project has elections, and is in short order going to announce a new Core Team.

Gentoo developers elect its Council, and the Foundation members (large overlap with the developers set) elect the Trustees.

Fedora.

The EU, for some value of 'elections'.