This is smm (aka smetamath), a library to read and manipulate .mm files used by
the Metamath System (http://us.metamath.org/).  It is written in Javascript
(ES6 using Babel), and is known to work with io.js (recommended) 2.2.1 and
2.0.1, as well as node.js 0.8.28 and 0.10.38.  node.js 0.12.4 displays a
strange test failure, I'd avoid it for smm.  It is distributed under the MIT
license (LICENSE).

To install prerequisites and use smm to verify a set.mm file:

1. Install nvm from https://github.com/creationix/nvm (this will hack your
shell rcfile, and only works with Bourneish shells on Unix; if not Unix, skip
this step)

2. Install io.js 2+ and npm via "nvm install iojs" (Unix); (There is an
official io.js installer for Windows.  This worked with the pre-Babel version
and may still work.)

3. Download dependencies with "npm install" with the current directory as the
smm checkout.

4. Run self-tests: npm test

5. Make node-babel available: npm install -g babel

6. Use it: node-babel misc/verify.js ../set.mm

7. Ahead of time testing (somewhat faster, use this for benchmarks):

$$$ mkdir out
$$$ babel lib -d out/lib
lib/ABRStringStore.js -> out/lib/ABRStringStore.js
lib/ConsoleErrorFormatter.js -> out/lib/ConsoleErrorFormatter.js
lib/MMOM.js -> out/lib/MMOM.js
lib/NodeIO.js -> out/lib/NodeIO.js
lib/Parser.js -> out/lib/Parser.js
lib/Scoper.js -> out/lib/Scoper.js
lib/Verifier.js -> out/lib/Verifier.js
$$$ babel misc -d out/misc
misc/abr_stress.js -> out/misc/abr_stress.js
misc/gen_expon.js -> out/misc/gen_expon.js
misc/line_stress.js -> out/misc/line_stress.js
misc/repl.js -> out/misc/repl.js
misc/verify.js -> out/misc/verify.js
$$$ node out/misc/verify.js .../set.mm/set.mm
parse 778 ms
scope 232 ms
parser 667 ms
verify 4422 ms