Heytools - JavaScript tools, AJAX tools and some fully server side tools.

MATLAB - A high-level language and interactive environment for numerical computation, visualization, and programming

WordCounter.net - Count words, sentences, paragraphs etc.

Wolfram Mathematica - Mathematica has characterized the cutting edge in specialized processing—and gave the chief calculation environment to a large number of pioneers, instructors, understudies, and others around the globe.

NimbleText - NimbleText is a text manipulation and code generation tool available online or as a free download.

Maxima - Maxima is a fairly complete computer algebra system written in Lisp with an emphasis on symbolic computation.