Arduino is an open source project supported by many.
Nicholas Zambetti has contributed since the beginning.
Yaniv Steiner and Giorgio Olivero have been supporting the project and are working at using it with the Instant Soup platform.
The Arduino platform used to include the avr-gcc tool chain, uisp, and the Procyon AVR-LIB by Pascal Stang.
The Arduino language syntax is based on Wiring by Hernando Barragan
The Arduino environment is based on Processing by Ben Fry and Casey Reas.
Thanks to all the people who are supporting arduino (Note July 2008 - This list needs to be updated, it's from 2005)