General:

Convert
Unit conversion program that will convert the most popular units of distance, temperature, volume, time, speed, mass, power, density, pressure, energy and many others.

OnlineConversion
Convert just about anything to anything else online.

Engineering Power Tools
Engineering programs and data tables (metric and U.S. units).

Euronorm.net
European laws and standardization regarding organization, engineering, maintenance, working environment, etc. (Dutch).

Tribology-abc
Information, software and tools for mechanical engineering.

Wikipedia
The free encyclopedia that anyone can edit.


Metalworking, tools and stuff:

G-M Codes
CNC G- and M-codes, common for most machines.

Collet Identification
Dimensions of some of the most common collets.

Taper Identification
Dimensions of some of the most common tapers.

Gewinde-normen.de
Specifications of (all?) International Thread Standards.


Electronics:

Datasheet Catalog
Online datasheet source for electronic components and semiconductors.

Proton Development Suite
Basic compiler from the British company Crownhill
The free Lite Edition has a restriction of 50 lines of valid BASIC code and only supports the 12C508, 12F675, 16F628A and 16F877 PIC microcontrollers.

Bumblebee
PIC programming software for Windows which can be used with the GalvaWisp ICSP programmer.

Eagle
Easy to use program for
designing printed circuit boards.
Includes a schematic editor, layout editer and autorouter.
The free Light-version is limited to 1 schematic sheet, 2 signal layers and 100x80mm routing area.

FreePCB
Freeware printed circuit board layout editor.

TinyCAD
Freeware p
rogram to draw circuit diagrams.



Technical information and downloads