| OPAL | ⊕ 1993 | ↓ ↑ ⊕ Specialised Languages | Goguen algebra | ⊕ Germany | Algebraic functional language |
| OPAL-0 | ⊕ 1993 | ↓ ↑ ⊕ String and List Processing | Goguen algebra | ⊕ Germany | Algebraic functional language |
| OPAL-1 | ⊕ 1993 | ↓ ↑ ⊕ Specialised Languages | Goguen algebra | ⊕ Germany | Algebraic functional language |