| Title | Publisher | Year | Language | Documents |
|---|---|---|---|---|
| Obscure Naturalist, The | Peter Hague | 1990 | English | |
| Odisea | Juana Pueblo Soft | 1990 | Spanish | |
| Ojo del Dragon, El | Wazertown Works | 1990 | Spanish | Map |
| One of Our Wombats is Missing | Zenobi Software |
1990 | English | Solution |
| Onyx | Utopia Software [1] |
1990 | Czech | |
| Opaline | Interactive Technology |
1990 | English | |
| Operation Blue Sunrise | Colin Campbell |
1990 | English | |
| Oppressed Land, The | Zenobi Software |
1990 | English | Solution, Hints |
| Oraculo, El | Javier De Miguel | 1990 | Spanish | Solution, Map |