| ID | Name | Type |
|---|---|---|
| #19735 | OK Software | - |
| #10494 | OKF | ? |
| #10495 | OMK Software S.L. | Z |
| #10496 | OMNI Publications International Ltd | Z |
| #10497 | ON1KLE | ? |
| #10498 | ON5KN | ? |
| #10499 | ON6LJ Software | Z |
| #19299 | ONOsoft | P |
| #22476 | ORAC81 | + |
| #17581 | ORT/GEC ITEC | R |
| #10500 | OSSoft | Z |
| #10501 | OVV Rack | ? |
| #10502 | OZ1BII | ? |
| #10503 | Oak Pictures | Z |
| #10504 | Oasis Software | P |
| #10505 | Oberon Group | Z |
| #15912 | Oberon International | Z |
| #10506 | Oblique Strategy | ? |
| #10507 | Obo | ? |
| #22763 | Obsolete.gr | - |