| ID | Name | Type |
|---|---|---|
| #10577 | Omycron Software | Z |
| #17588 | Once Bytten | S |
| #19330 | Ondra Topinka | + |
| #22480 | Ondřej Kafka | + |
| #20185 | Ondřej Kárný | + |
| #10578 | Ondřej Mihula | + |
| #19286 | Ondřej Novák | + |
| #19310 | Ondřej Pavelka | + |
| #10579 | Ondřej Svatý | + |
| #15914 | One Percent Screens | Z |
| #10580 | One Week Productions | Z |
| #10581 | Oni Records | Z |
| #22144 | Oniric Factor | P |
| #10582 | Online PLC | Z |
| #10583 | Onspec Software | Z |
| #10584 | OpalSoft | Z |
| #10585 | Open University | Z |
| #10586 | Opera Soft S.A. | Z |
| #21358 | Oporto BBS | P |
| #10587 | Optical Brothers | Z |