Zalo is a messaging app developed by VNG Corporation, a company based in Ho Chi Minh City, Vietnam. It offers chats and communication with contacts for individuals and groups, and is delivered as an application operated by the vendor. Its website describes it as a communication app. VNG is the parent company of Zalo.
Vietnam is outside the EU, so the operator falls under Vietnamese law. The vendor's public pages do not state where user data is stored; organisations should request this in writing. For a European organisation the key questions are where messages and metadata reside, which authorities can request access, and what contractual safeguards are available. The service is mainly relevant where contacts in Vietnam use it. Public information is limited, so contractual and technical due diligence matters before any business use.