O2
Oaklisp
OBE
Oberon
Oberon-1
Oberon-2
Oberon-V
OBJ
OBJ0
OBJT
OBJ1
OBJ2
OBJ3
Object CHILL
Object Lisp
ObjectLOGO
Object Oberon
Object-CHILL
Object-COBOL
Object-Oriented Turing
ObjectPAL
Object Pascal
Object-Z
Objective C
Objlog
ObjVlisp
ObjVProlog
Obliq
Oblog
OBSCURE
Oc
OCAL
occam 1
occam 2
occam 3
OCL
OCODE
Octave
odl
OIL[1]
OIL[2]
OISC
OLC
OLDAS
OLGA
Omega
OMNICODE
OMNIFAX
Omnimark
OMNITAB
Ondine
Ontic
OO-CHILL
OOF
OOPS
OOT
OOZE
OPAL-0
OPAL[1]
OPAL[2]
OPAL[3]
OPAL[4]
OPAL[5]
O-plan
OPS[1]
OPS[2]
OPTRAN
Orca
OREGANO
Orient84/K
ORTHOCARTAN
Orthogonal
Orwell
OSCAR[1]
OSCAR[2]
O'small
OSQL
OSSL
Ottawa Euclid
OWHY
OWL
Ox
Oz
oz++