Scratchbox 2 (often abbreviated to "sb2" or "sbox2") is a cross-compilation toolkit designed to make embedded Linux application development easier. It also provides a full set of tools to integrate and cross-compile an entire Linux distribution.
In the Linux world, when building software, many parameters are auto-detected on the host system (like installed libraries and system configuration), for example through Autotools' ./configure scripts. When one wants to build software for an embedded target by cross-compilation, most auto-detected parameters are incorrect: I.e. host configuration is not the same as the embedded target's configuration, hence the name cross-compilation.
Without Scratchbox 2, one has to manually set many parameters and "hack" the "configure process" to generate working executable code for the embedded target.
Scratchbox 2 allows one to set up a "virtual" environment that will trick Autotools and other executables into thinking that they are directly running on the embedded target with its configuration.
Moreover, Scratchbox 2 provides a technique called "CPU-transparency" that goes further: With "CPU-transparency", executables built for the host CPU or for the target CPU could be executed directly on the host with sb2 handling the task to emulate a different CPU-architecture if necessary to run software components compiled for the target CPU. Hence a build process can mix using programs built for different CPU-architectures. That is especially useful when a build process requires to build a software component first as a build dependency for building another software component: For example, a "Lexer" must be built first in order to generate code for / of another software component with it.
BinChengfei/scratchbox2 at GitHub provides an unaltered mirror of the former Scratchbox 2 Git repository at Gitorious with its latest Git tag being 2.3.90 on 2012-09-05.lbt/scratchbox2 (up to tag pkg-mer-2.3.90-4 on 2013-04-25) and mer-packages/scratchbox2 (up to tag 2.3.90-git2 on 2014-03-05), both at GitHub, show intermediate states before the Nemo / Mer merger, when Scratchbox 2's active source tree was moved to the now dissolved git.merproject.org.git.merproject.org/mer-core/scratchbox2 is sailfishos/scratchbox2 at GitHub, which contains all commit history and Git tags of all aforementioned Git repositories.