QuantLib is a cross-platform, quantitative finance C++ library for modeling, pricing, trading, and risk management in real-life. It is also wrapped as Python/Ruby/Scheme modules. Extensions for Excel, R, and Mathematica are available. Other such extensions are under consideration. QuantLib offers tools that are useful both for practical implementation and for advanced modeling. It features market conventions, yield curve models, solvers, PDEs, Monte Carlo (low-discrepancy included), exotic options, VAR, and so on.
MPI Ruby is a Ruby binding of MPI. The primary goal in making this binding was to make the power of MPI available to Ruby users in a way that fits into the language's object oriented model. In order to do this, the buffer and datatype management necessary in the C, C++, and Fortran bindings have been removed. What this means is that MPI Ruby allows you to treat objects as messages. MPI Ruby also aims to be a complete binding to MPI, in that it offers access to nearly all functionality of MPI.
PhysicsFS is a library to provide abstract access to various archives. The programmer defines a "write directory" on the physical filesystem. No file writing done through the PhysicsFS API can leave that write directory, for security. For file reading, the programmer lists directories and archives that form a "search path". Once the search path is defined, it becomes a single, transparent, hierarchical filesystem. This makes for easy access to ZIP files in the same way as you access a file directly on the disk, and it makes it easy to ship a new archive that will override a previous archive on a per-file basis. Symbolic links can be disabled, for added safety. Finally, PhysicsFS gives you a platform- abstracted means to determine if CD-ROMs are available, the user's home directory, where in the real filesystem your program is running, etc.
MetaRuby contains miscellaneous libraries (useful now) for a future Ruby-in-Ruby interpreter including Array/Hash/String as abstract ("Hollow") classes, an undo queue, a statistical time-profiler, an event loop, a modular marshaller ("ToSource"), a specification for a modular+reflexive+homoiconic remote call system ("LGRAM"), a declarative type system, a schema for expressing Ruby source code as proper (non-special) Ruby objects, etc.
Ruby-GConf allows Ruby developers to write applications that store their configuration data using GConf (1.0.x). GConf is a configuration database system written by Havoc Pennington et al, and part of the GNOME application development framework (although it can be used separately).
JTTui is a Ruby library for text mode user interfaces based on the curses library. It should work on most Unix-like systems. Because this library is written in Ruby, it follows the object paradigm in the native Ruby way. It contains widgets like dialogs, buttons, checkboxes, listboxes, and trees. The licence is the same as Ruby, allowing use of the GNU GPL or one less restrictive.
Ruby/Google offers a higher-level abstraction of Google's SOAP-driven Web API. It allows the user to programatically query the Google search engine from Ruby. The aim of the library is to shield the programmer from the details of the raw data structures returned by the Web API, and in the process make the API more accessible for everyday use.