Siena:

Octocom
Octopus Energy Group
Oliver James Associates Ltd.
Omnissa (Italy) S.r.l.
Oncode
OneOcean Group
OneStream Software LLC
oneway promotion
Onyx Technology S.r.L.
Opdenergy
Open Smart Services
Open-Xchange Inc.
openjobmetis
OPLIUM
OralPro
Orbyta Group
Orchard Robotics
orienta
Orienta SPA
ottosunove
Out in Science, Technology, Engineering, and Mathematics
outsourcing group
OutSystems, Inc.
OVERTECH Consulting
OVS S.p.A.
Oxford Instruments
Oxigent Technologies