S²LOW (Service Sécurisé Libre inter-Opérable pour la Vérification et la Validation) is a teletransmission platform for documents that French local authorities and other public bodies regularly exchange with their partners and supervisory authorities. It covers two flows: the ACTES protocol sends administrative and budget acts to the prefecture for legality review, and the Helios module handles accounting flows under the PES v2 protocol. According to the vendor, S²LOW provides encrypted transfers, certificate-based sender authentication, timestamping, recording of the flows exchanged and verification of electronic signatures.
S²LOW has been developed since 2006 by Libriciel SCOP, a French cooperative based in Castelnau-le-Lez that builds free software for the public sector. The software is free software and can be deployed in three ways: on the shared platform of the association ADULLACT, through other public or private teletransmission operators, or in-house by an organisation after prior approval. Libriciel also offers installation, support and hosting. A European public body can therefore keep the service under its own or French control.