| O-to-i-re - Dreamcast Sequencer | JP | 1999-12-09 |
Waka Manufacturing | Commercial |
| Official Sega Dreamcast Magazine Vol. 10 - January 2001 | US | 2001 |
| Commercial |
| Official Sega Dreamcast Magazine Vol. 11 - February 2001 | US | 2001-02 |
| Commercial |
| Official Sega Dreamcast Magazine Vol. 2 - November 1999 | US | 1999-11 |
| Commercial |
| Official Sega Dreamcast Magazine Vol. 3 - January 2000 | US | 2000-01 |
| Commercial |
| Official Sega Dreamcast Magazine Vol. 4 - March 2000 | US | 2000-03 |
| Commercial |
| Official Sega Dreamcast Magazine Vol. 5 - May 2000 | US | 2000-05 |
| Commercial |
| Official Sega Dreamcast Magazine Vol. 6 - July 2000 | US | 2000-07 |
| Commercial |
| Official Sega Dreamcast Magazine Vol. 7 - September 2000 | US | 2000-09 |
| Commercial |
| Official Sega Dreamcast Magazine Vol. 8 - November 2000 | US | 2000-11 |
| Commercial |
| Official Sega Dreamcast Magazine Vol. 9 - December 2000 | US | 2000-12 |
| Commercial |
| Omikron - The Nomad Soul | US | 2000-06-22 |
Eidos Interactive | Commercial |
| Omoide ni Kawaru Kimi - Memories Off | JP | 2002-11-28 |
KID | Commercial |
| Ooga Booga | US | 2001-09-11 |
Sega | Commercial |
| Oogami Ichirou Funtouki - Sakura Taisen Kayou Show Beni Tokage yori | JP | 2000-02 |
Sega | Commercial |
| Orange Pocket - Cornet | JP | 2004-04-28 |
Pionesoft | Commercial |
| Orion's Puzzle Collection | EU | |
OrionSoft | Unlicensed |
| Ouka Houshin - Ouka Sakishi Toki | JP | 1999-12 |
Media Works | Commercial |
| Outtrigger | EU | 2001-08-03 |
Sega | Commercial |
| Outtrigger | JP | 2001-08-02 |
Sega | Commercial |
| Outtrigger | US | 2001-07-24 |
Sega | Commercial |