They slip, they slide, they're considered obsolete, but they don't need batteries, and are unaffected by computer viruses...
Dover publishes a lot of older math texts that are no longer being published by the "first string" publishers such as Addison Wesley, Prentice Hall, and Springer Verlag. As a result, the Dover texts are not new. There are a lot of texts from the 1950s and 1960s. Of course, many of the mathematical principles known then are still relevant today, and I've run through some of these "old texts" and found that they bore remarkable resemblance to the vastly-more-expensive texts I studied from in university.
Difference Equations to Differential Equations: An introduction to calculus
This is a Calculus textbook that is distributed under the terms of the GPL.
Fundamental Problems in Algorithmic Algebra (including Continued Fractions!)
Professor W Kahan's Supplementary notes for MATH 128
On numerical analysis and round-off errors
The Gestalt System project at SourceForge
Plans to be a "data analysis" system that might be reminiscent of SAS, combining:
Numerical and Statistical Methods with SCILAB for Science and Engineering - Volumes 1 and 2
Has a lot of links to add-ins for MATLAB, Microsoft Excel, as well as to code in C/C++ , Fortran , and Java.
Math for the Layman - by Ken Iverson, creator of Section 7.6 and .
A symbolic math system written in Common Lisp based on MACSYMA.
A Scheme-based algebra package.
GiNaC is Not a CAS (Computer Algebra System) - Plans to replace Maple in some applications
UC Berkeley Computer Algebra Papers
Including a critique of Mathematica...
XLOOPS - program that uses Maple to calculate Feynman diagrams
To the user, this somewhat resembles Mathematica, but has the advantage of being totally open (full source code). One can manipulate polynomials in several variables over the integers, rational functions, and a variety of other mathematical objects. Manipulations include simplification, differentiation, integration, evaluation, pattern matching, etc. Written in Common Lisp
Kalamaris - a mathematics research framework using KDE providing symbolic algebra capabilities.
A = B - on Computer Algebra
This is the study of the strategy of conflicts; it was formalized in the analysis of strategies for nuclear war, but the analysis can be used to frame a wide scope of issues.
The common problems of Game Theory include The Prisoners' Dilemna and Zero sum games. Much contention arises over what sum a particular "game" comes to...
In 1948 and 1949 Kenneth J. Arrow conducted research on the theory of social choice (group decision making or voting). He investigated the possibility of a method of voting which would embody the following desirable features:
Universality.
The voting method should provide a complete ranking of all alternatives from any set of individual preference ballots.
Monotonicity criterion.
If one set of preference ballots preference ballots would lead to an an overall ranking of alternative X above alternative Y and if some preference ballots are changed in such a way that the only alternative that has a higher ranking on any preference ballots is X, then the method should still rank X above Y.
Criterion of independence of irrelevant alternatives.
If one set of preference ballots would lead to an an overall ranking of alternative X above alternative Y and if some preference ballots are changed without changing the relative rank of X and Y, then the method should still rank X above Y.
Citizen Sovereignty.
Every possible ranking of alternatives can be achieved from some set of individual preference ballots.
Non-dictatorship.
There should not be one specific voter whose preference ballot is always adopted.
Arrow concluded that it is not possible to have a voting method with all of these properties. The conditions are mutually contradictory.
More simply put, there is no consistent method of making a fair choice among three or more candidates. This result assures us that there is no single election procedure that can always fairly decide the outcome of an election that involves more than two candidates or alternatives.
The impact of this theorem is that people find themselves, whether from perspectives of moral obligation or reasonableness, wanting things that are downright impossible.
In 1972 Arrow won the Nobel Prize in economics for his many contributions to that field, including this theorem.
Perhaps of somewhat nominal connection; pricing of products is a big, hairy, complex problem. There's a lot of " Prisoner's Dilemma" to it, and actually understanding why it is so troublesome likely requires some mathematical sophistication...