Feel free to add your own SpiderMonkey-based open source projects (and if necessary add categories)!

Wrappers / bindings

C++

• Cocos2d-JS - Cocos2d-JS is a cross-platform Game Engine which embeds SpiderMonkey, providing the same API for both web and native platforms. Getting started here.
• Flusspferd - (newer) C++ bindings
• libjspp - C++ template based library for extending & embedding SpiderMonkey; works with SpiderMonkey 1.8.5 and above, has lots of goodies
• Spiderape - the oldest C++ bindings for SpiderMonkey
• TriXUL - (TriXUL CVS) - Trixul XML-based GUI toolkit embeds SpiderMonkey, using JavaScript to implement logic behind its GUI, supporting calls from JavaScript to C++ objects

Rust

• mozjs - Rust bindings used by Servo

GNOME

• gjs - JavaScript bindings to GNOME (broadly, to any library using the GObject introspection mechanism)

Objective Caml

• http://alain.frisch.fr/soft.html#spider - bindings to embed SpiderMonkey in OCaml applications

Perl

• http://jspl.msg.mx/ - bindings to cross-embed SpiderMonkey and Perl. Includes a JS shell that allows you to use CPAN modules from JavaScript.

Python

• http://pypi.python.org/pypi/python-spidermonkey

wxWidgets

• GLUEscript (formerly wxJavaScript)

Code generators

• jsapigen - generates bindings for embedding SpiderMonkey in C applications

Extensions

• http://code.google.com/p/jslibs/ - zlib, SQLite, NSPR, ode, libpng, libjpeg, libffi, (...) libraries for SpiderMonkey

• http://www.jsdb.org/ - a JS Shell with native objects for files, networks, databases, compression, email, etc.

• http://code.google.com/p/gpsee/ - commonJS platform, native-language module interoperability methods, modules, etc. for SpiderMonkey. Designed to supplement existing embeddings, GPSEE ships with a sample trivial embedding, a scripting host, and an augmented version of Mozilla's JS Shell. Bundled modules include support for ByteArray, ByteString, CGI, POSIX Signals, FFI, and more.

• http://javalikescript.free.fr/ - a general-purpose JavaScript platform that aims to provide an extensible tooling framework

• http://www.synchro.net/ - a telnet/SSH bulletin board system (BBS) and internet server (HTTP/SMTP/FTP) with extra Internet services written in JavaScript (IRC, IMAP, Gopher, and many more)

• https://github.com/mindbit/libjssql/wiki - a library that aims to provide a generic SQL API for JavaScript that is as similar as possible to JDBC

Miscellaneous

• ServerJS, a standardization effort for the fragmented Server-side Javascript world
• 0 A.D., historical RTS game with JavaScript scripting
• http://soubok.googlepages.com/javascript
• Malzilla - tool for hunting malware by deobfuscating JavaScripts on web pages, using SpiderMonkey