BlueZ is the Bluetooth stack implemented in most Linux kernels.

Its goal is to make an implementation of the Bluetooth wireless standards specifications for Linux.
As of 2006, the BlueZ stack supports all core Bluetooth protocols and layers.
It was initially developed by Qualcomm and is available for Linux kernel versions 2.4.6 and up.

For user space applications, BlueZ essentially provides two ways to implement the stack in the application: Through DBus or through the so-called MGMT API. These methods are high- and low level respectively.

In addition to the basic stack, the bluez-utils and bluez-firmware packages contain low-level utilities such as dfutool, which can interrogate the Bluetooth adapter chipset to determine whether its firmware can be upgraded.

Further information about BlueZ:

Aditionally there are two IRC channels available on freenode.net where you can find developers and other users of BlueZ:

#bluez (development related topics)
#bluez-users (non-development related topics)