What is boost?

[Mario Valentino]

I've heard about this library but why everyone loves it??
Do you have any tutorial ?

[JLBorges]

Boost is not one library; it is a collection of several libraries.
http://www.boost.org/users/index.html

Boost libraries are documented; most of the boost libraries provide a tutorial introduction.

An introductory e-book covering many boost libraries: http://theboostcpplibraries.com/

[keskiverto]

At least some of Boost content has become "advanced, tried and true" to the level that the current C++ standard library now has more or less verbatim copies of them.

Is Boost popular because it is good, or is it good due to natural pressure of popularity? A bit of both, I suppose.