| OPAK | 1968 | On-Line | Other Conversational | United States | |
| OPAL | 1993 | Specialised Languages | Goguen algebra | Germany | Algebraic functional language |
| OPAL | 1972 | Specialised Languages | Other algorithmic | United States | |
| OPAL | 1984 | Business Data Processing | OO DBMS | United States | Previous name of Smalltalk DB |
| OPAL | 1960 | Business Data Processing | Flat DB | United Kingdom | CEIR data processing language |
| OPAL | 1989 | Specialised Languages | DSP | United States | |
| OPAL | 1975 | ||||
| OPAL | 1963 | Excluded from Sammet | Symbolic assemblers | United States | Philco symbolic assembler |
| OPAL-0 | 1993 | String and List Processing | Goguen algebra | Germany | Algebraic functional language |
| OPAL-1 | 1993 | Specialised Languages | Goguen algebra | Germany | Algebraic functional language |
| OPAL2 | 1995 | Germany |