Other
- OPA co. ltd. (oriental park avenue), a Japanese clothing retail chain and subsidiary of Daiei
- Oligo Pool Assay, a SNP genotyping platform from Illumina
- Online Privacy Alliance, a coalition of Internet companies
- Opa (programming language), a web development platform
- Open Platform Architecture, a software interface from Ericsson Mobile Platforms for use internally in cellular phones
- Optical parametric amplifier, a method to amplify laser light
- Oracle Policy Automation, an enterprise applications suite
- Ordre des Palmes Academiques, an Order of Chivalry of France for academics and cultural and educational figures
- Oregon Potters Association, not-for-profit group of clay artists
- Opa, the nickname of Dorus Rijkers, Dutch lifeboat-captain who rescued over 500 people in the course of his career
- OPA, a mixture used in chemical weapons such as M687
- ortho-phthalaldehyde, a chemical compound
- Opa, Dutch or German informal word for grandfather
- Opa!, a film starring Matthew Modine and Agni Scott
- Postnominal letters used by the Anglican Order of Preachers (Ordo Praedicatorum Anglicanus)
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