From Rosegarden Developer Website:
"Rosegarden is a professional audio and MIDI sequencer, score editor, and general-purpose music composition and editing environment.
Rosegarden is an easy-to-learn, attractive application that runs on Linux, ideal for composers, musicians, music students, and small studio or home recording environments."
Rosegarden Screenshot:

Download Rosegarden
Rosegarden General Resources
Rosegarden Tour
Rosegarden Tutorial
Rosegarden Documentation
Rosegarden Support
Rosegarden Hardware and System Requirements
Rosegarden FAQs
Other Links Regarding Rosegarden:
Rosegarden Free Companion (Online Resource Book)
Rosegarden Links
Rosegarden Mailing Lists
Rosegarden Authors
Rosegarden on Sourceforge
Rosegarden Freshmeat Listing
Rosegarden Reviews:
Rosegarden Review on Linux Dev Center
Languages Supported:
Russian, German, Spanish, French, Italian, Estonian, Welsh, Swedish, Dutch, Japanese, Simplified Chinese, Czech, and Catalan