This is evolved into a patch set for mknetrel. Spring 2005: In a bold move a set of patches for MinGW are created to build LilyPond and all its  dependencies. Simultaniously, a cross build environment and installer for MacOSX is created.
Creating a cross build environment is not too difficult, esp. not if you know how to use Google. The problem is that they always break and never work on other machines. GUB starts as an effort to unify the Windows and MacOS builders and to make the process somewhat dependable and reproducible, i.e.: even more free time for the developers (if there is such a thing) as the builds always succeed. It uses Python instead of make and bash and adds checksums for the package build specs. The unification of cross builds greatly facilitates adding of new architectures and before long GUB supports cross building lilypond binaries for 9 different platforms.
GUB2 adds serialization of the Python build code before execution. This makes the build checksumming less coarse, ie, less gratuitous rebuilds and more reliable. Also, all Python code is executed before the build process starts, which means that there is less chance of silly run time errors. Lots of packages are added in an effort to replace the OpenEmbedded-based build system for the Samco 3G video phone at SES, Philips Research Eindhoven.
In Novell's Hackweek-iii GUB enters into its Third Life with GUB3, adding cross-platform build dependencies and patches for an OpenOffice.org MinGW cross build, including all essential libraries. Later, Inkscape is added, exploring and implementing x.org dependencies. After that, building a windows installer for GNU Denemo took only one day, including all dependencies.
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