Backtrack is Linux distribution based on Ubuntu for digital forensics and penetration testing created by Offensive Security team. Backtrack provides large collection of security-related tools including Metaslopit, Aircrack-ng. Wireshark, Nmap, Ophcrack and more. The last version (5 R3) was released in August 2012.
After last version, Offensive Security team created Kali linux - Backtrack successor based on Debian.