| Title | Publisher | Year | Language | Documents |
|---|---|---|---|---|
| Ogres | Alan DeNiro | 2003 | English | |
| On a Horse with No Name | Greg Ewing | 2000 | English | Solution |
| Onaar | Robert DeFord | 2015 | English | Solution |
| Oskar und der Tod | Uwe Pilz | 1997 | German | |
| Out of the Study | Anssi Räisänen | 2002 | English | Solution, Map |