DragonFly BSD is a free BsdUnix operating system that started in 2003 as a fork of FreeBsd 4.8. DragonFly started over an alternate SMP synchronization strategy than the one FreeBSD 5 ('SMPng') was moving towards - where FreeBSD was splitting the big kernel lock into many small locks, DragonFly moved many resources to per-CPU pools and used inter-CPU messaging for communication. 

DragonFly has gained a number of cool features over the years - a snapshotting filesystem, HAMMER, process checkpointing, virtual kernels. 

Its homepage is located, predictably enough, at http://www.dragonflybsd.org/

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CategoryOperatingSystem CategoryUnix