Ro or RO may refer to:

• Ragnarok Online, a South Korean computer game
• Red Orchestra: Ostfront 41-45, an American computer game
• Regnum Online, an Argentinian computer game
• RO (game), an American puzzle video game

Rø is a small community on the Danish island of Bornholm, 2 km from the north coast and 7 km west of Gudhjem. The Rønne–Allinge railway (1913–1953) brought prosperity to the village leaving the old station in the village. The Bornholm Art Museum is close to Rø as are the scenic Sanctuary Rocks.

.ro is the Internet country code top-level domain (ccTLD) for Romania. It is administered by the National Institute for R&D in Informatics. As of December 2007, about 250,000 domains were registered under the .ro domain. In June 2008 there were around 6.8 million Google results for the .ro domain. On June 2012 there were 732,867 .ro domain names.

Martha is a layout engine used in enterprise applications to create HTML and XML editing and rendering applications in Java. The framework is used in all of the RealObjects applications: PDFreactor, Nimbudocs Editor, and edit-on NG developed; and is the successor to WordPerfect. The Martha framework is also made available for OEM and project-based licensing and is used by the U.S. Army, Vizrt, Objective Corporation Limited, Neota Logic, European Patent Office, Infoland a Dutch independent software vendor, Pulinco Engineering AG, SafeHarbor Technology, Gentleware AG, DZ Bank AG, DSV, and the University of Paderborn.

Rö Church is a medieval Lutheran church in the Archdiocese of Uppsala in Stockholm County, Sweden.