| Oncode S.r.l. | |
| Oncoxx Biotech S.r.l. | |
| Ondenet | Rimini |
| ONdesign S.r.l. | |
| One AM S.r.l. | |
| One On Line | Salerno |
| Onebip S.p.A. | Milan |
| Onedirect | Milan |
| OneTray S.p.A. | |
| OnLine Common Sense | Caserta |
| Onyon S.r.l. | |
| oobe-xr S.r.l. | |
| OPByte Software | Rome |
| Open Accelerator | Milan |
| Open Data S.r.l. | Bologna |
| Open Fiber S.p.A. | |
| Open IT S.r.l. | Trento |
| Open Lab S.r.l. | Florence |
| Open Observatory of Network Interference | |
| Open S.a.s. | Padua |
| Open Seed S.r.l. | |
| Open1 S.r.l. | Ferrara |
| Openkey S.r.l. | Ascoli Piceno |
| OpenMall S.r.l. | |
| OpenVOIP | Rome |
| Opificio137 | |
| Opis S.r.l. | |
| Opocrin S.p.A. | |
| Opstart S.r.l. | |
| Optea S.r.l. | Bologna |
| Optima S.r.l. | Bologna |
| Opto Engineering S.r.l. | Mantua |
| Opyn | Milan |
| Oraigo S.r.l. | |
| Orange Drop Design | Latina |
| Orga System | Milan |
| Orimos.dev S.r.l. | Venice |
| ORMU di Fenini S.p.A. | Parma |
| ORS S.r.l. | |
| Orwell VR | Milan |
| Outdoora | |
| Oval.it | Bergamo |
| Over Holding S.r.l. | Friuli-Venezia Giulia |
| Overbi S.r.l. | |
| OVERSOFT | |
| Oversonic S.r.l. | |
| Overzoom | |
| Ovolab | Turin |
| OxyTech S.r.l. | Milan |
| P&L Sistemi | Padua |