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Think Blue Linux (sometimes ThinkBlue Linux) was a port of Linux to IBM S/390 (later, zSeries) mainframe computers, done by the Millenux subsidiary of German company Thinking Objects Software GmbH.

The distribution consisted primarily of a collection of Red Hat Linux 6.1 packages (or RPMs) on top of IBM's port of the Linux kernel. Distribution of the product ceased on February 16, 2006.