GIMP Manual
The GIMP is the GNU Image Manipulation Program, a freely distributed piece of software suitable for such tasks as photo retouching, image composition and image authoring, similar to Adobe Photoshop, but running on X Window system on Unix/Linux platforms.
Getting started with TeX and LaTeX
Good Starters at TeX Users Group.
Hypertext Help with LaTeX
A wonderful LaTeX manual in NASA.
Debian User Documentation
Debian is a free, or Open Source, operating system (OS).
The Mathematica Documentation Center
On www.wolfram.com, the creator of Mathematica.
Eric Weisstein's world of Mathematics
MathWorld is a convenient, comprehensive, and interactive mathematics encyclopedia intended for students, educators, math enthusiasts, and researchers. Like the vibrant and constantly evolving discipline of mathematics, this site is continuously updated to include new material and incorporate new discoveries.
MATLAB help desk
On www.mathworks.com, the developer of Matlab.
Handbook of Space Astronomy and Astrophysics
On-line version of Martin V. Zombeck's Handbook of Space Astronomy &s; Astrophysics.
Physical Reference Data
Physical Reference Data at National Institute of Standards and Technology.
GNU Manuals Online
GNU Manuals on Free Software Foundation site www.gnu.org.
Pine User's Guide
The default email reader on most NYU systems (SCIRES, IS, ...).
FreeBSD Hypertext Man Pages
Searches for man pages on many Unix-like systems (BSD, Linux, Unix, ULTRIX etc).
Oracle Product Documentation
Java documentation.
W3schools HTML Tutorial
Simple interactive HTML tutorial. Also have tutorials for CSS, PHP and Javascript.