Ren-C is a branch of the Apache 2.0 open-sourced Rebol 3 codebase.

The goal of the project isn't to be a "new" language, but to solve many of the outstanding design problems historically present in Rebol. Several of these problems have been solved already. For progress and notes on these issues, a Trello board is semi-frequently updated to reflect a summary of changes.

The project's name comes from the idea that it is a C implementation of the "REadable Notation" (a name given to Rebol's file format). It is deliberately transitional--because rather than be a brand or product in its own right, Ren-C intends to provide smooth APIs for embedding an interpreter in C programs...hopefully eventually rebol.exe itself.

One of these APIs (libRebol) is "user-friendly" to C programmers, allowing them to avoid the low-level concerns of the interpreter and just run snippets of code mixed with values, as easily as:

int x = 1020;
REBVAL *negate = rebValue("get 'negate");  // runs code, returns value

rebElide("print [", rebI(x), "+ (2 *", negate, "358)]");

// Would print 304--e.g. `1020 + (2 * -358)`, rebElide() returns C void.

The other API (libRebolCore) would offer nearly the full range of power that is internally offered to the core. It would allow one to pick apart value cells and write extensions that are equally efficient to built-in natives like REDUCE. This more heavyweight API would be used by extensions for which performance is critical.

The current way to explore the new features of Ren-C is using the r3 console. It is significantly enhanced from the open-sourced R3-Alpha...with much of its behavior coming from userspace Rebol code (as opposed to hardcoded C). In addition to multi-line editing and UTF-8 support, it can be "skinned" and configured in various ways, and non-C programmers can easily help contribute to enhancing it.

A C++ binding is also available, and for those interested in a novel application of this code, they might want to see the experimental console based on it and Qt: Ren Garden.

In doing this work, the hope is to provide an artifact that would rally common usage between the mainline builds, community builds, and those made by Atronix Engineering and Saphirion AG.

To promote community's participation in public forums, development discussion for Ren-C generally takes place in the Rebol* StackOverflow Chat.

There is a Discourse forum available for more long-form discussion.

It's also possible to contact the developers via Ren-C GitHub Issues. This should be limited to questions regarding the Ren-C builds specifically, as overall language design wishes and debates in the rebol-issues repository of Rebol's GitHub.

Ren-C does not require GNU Make, CMake, or any other make tools. It only needs a copy of a Ren-C executable to build itself. To do a full build, it can just invoke a C compiler using the CALL facility, with the appropriate command lines.

Several platforms are supported, including Linux, Windows, OS X, Android, and support for JavaScript via Webassembly. Configurations for each platform are in the %configs/ directory. When the build process is run, you should be in the directory where you want the build products to go (e.g. %build/). Here is a sample of how to compile under Linux:

# You need a Ren-C-based Rebol to use in the make process
# See %tools/bootstrap-shim.r regarding what versions are usable
# Currently there are usable executables in %/prebuilt ...
# ...but that's not a permanent solution!
#
~/ren-c$ export R3_MAKE="$(pwd)/prebuilt/r3-linux-x64-8994d23"

~/ren-c$ cd build

~/ren-c/build/$ "$R3_MAKE" ../make.r \
    config: ../configs/default-config.r \
    debug: asserts \
    optimize: 2

For a list of options, run %make.r with --help.

Though it does not require other make tools, it is optional to generate a makefile target, or a Visual Studio solution. %make.r takes parameters like target: makefile or target: vs2017. But there are several complicating factors related to incremental builds, due to the fact that there's a large amount of C code and header files generated from tables and scans of the source code. If you're not familiar with the source and what kinds of changes require rebuilding which parts, you should probably do full builds.

As a design goal, compiling Ren-C requires very little beyond ANSI C89. Attempts to rein in compiler dependencies have been a large amount of work, and it still supports a number of older platforms. However, if it is compiled with a C++ compiler then there is significantly more static analysis at build time, to catch errors.

(Note: The build process is much more complicated than it should be, but other priorities mean it isn't getting the attention it deserves. It would be strongly desirable if community member(s) could get involved to help streamline and document it! Since it's now all written in Rebol, that should be more possible--and maybe even a little "fun" (?))