This article is from the Vegetarianism FAQ, by firstname.lastname@example.org (Michael Traub) with numerous contributions by others.
Gelatin (used to make Jell-o and other desserts) is the boiled bones
of animals. An alternative substance is called Agar-Agar, which is
derived from seaweed. Another is made from the root of the Kuzu.
Agar-Agar is sold in noodle-like strands, powder, or in long blocks,
and is usually white-ish in colour. Some Kosher gelatines are made
with agar-agar, some are not. Some things that are vegan that are
replacing gelatin are: guar gum and carageenan. Only some
'emulsifiers' are vegan.