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+Scalar
+======
+
+Scalar is a repository management tool that optimizes Git for use in large
+repositories. It accomplishes this by helping users to take advantage of
+advanced performance features in Git. Unlike most other Git built-in commands,
+Scalar is not executed as a subcommand of 'git'; rather, it is built as a
+separate executable containing its own series of subcommands.
+
+Background
+----------
+
+Scalar was originally designed as an add-on to Git and implemented as a .NET
+Core application. It was created based on the learnings from the VFS for Git
+project (another application aimed at improving the experience of working with
+large repositories). As part of its initial implementation, Scalar relied on
+custom features in the Microsoft fork of Git that have since been integrated
+into core Git:
+
+* partial clone,
+* commit graphs,
+* multi-pack index,
+* sparse checkout (cone mode),
+* scheduled background maintenance,
+* etc
+
+With the requisite Git functionality in place and a desire to bring the benefits
+of Scalar to the larger Git community, the Scalar application itself was ported
+from C# to C and integrated upstream.
+
+Features
+--------
+
+Scalar is comprised of two major pieces of functionality: automatically
+configuring built-in Git performance features and managing repository
+enlistments.
+
+The Git performance features configured by Scalar (see "Background" for
+examples) confer substantial performance benefits to large repositories, but are
+either too experimental to enable for all of Git yet, or only benefit large
+repositories. As new features are introduced, Scalar should be updated
+accordingly to incorporate them. This will prevent the tool from becoming stale
+while also providing a path for more easily bringing features to the appropriate
+users.
+
+Enlistments are how Scalar knows which repositories on a user's system should
+utilize Scalar-configured features. This allows it to update performance
+settings when new ones are added to the tool, as well as centrally manage
+repository maintenance. The enlistment structure - a root directory with a
+`src/` subdirectory containing the cloned repository itself - is designed to
+encourage users to route build outputs outside of the repository to avoid the
+performance-limiting overhead of ignoring those files in Git.
+
+Design
+------
+
+Scalar is implemented in C and interacts with Git via a mix of child process
+invocations of Git and direct usage of `libgit.a`. Internally, it is structured
+much like other built-ins with subcommands (e.g., `git stash`), containing a
+`cmd_<subcommand>()` function for each subcommand, routed through a `cmd_main()`
+function. Most options are unique to each subcommand, with `scalar` respecting
+some "global" `git` options (e.g., `-c` and `-C`).
+
+Because `scalar` is not invoked as a Git subcommand (like `git scalar`), it is
+built and installed as its own executable in the `bin/` directory, alongside
+`git`, `git-gui`, etc.