Other
- K-9 (film), starring James Belushi
- K-9 (Kansas highway), a state highway in the U.S. state of Kansas
- K9 Web Protection, Web content control software
- K-9 Mail, a mail client for the Android (operating system), also called k9 or k9mail
- K9Copy, a DVD backup and authoring program for Unix-like OSs (GNU/Linux and BSD)
- KNIN-TV, the CW affiliate in Boise, Idaho that was known as K9 in the late 1990s
- K-9 (missile), a long-range air-to-air missile developed by the Soviet Union in the late 1950s
- K-9 (TV series) a British/Australian comedy/adventure series starring the same character as featured in Doctor Who as listed above.
- K9 Cisco, a denotation of licensing and image files with AES/3DES features enabled
- Violin Sonata No. 4 (Mozart) K. 9, by Wolfgang Amadeus Mozart
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