Pydio

Pydio Cells, previously known as just Pydio and formerly known as AjaXplorer, is an open-source file-sharing and synchronisation software that runs on the user's own server or in the cloud.
Presentation.
The project was created by musician Charles Du Jeu (current CEO and CTO) in 2007 under the name AjaXplorer. The name was changed in 2013 and became Pydio (an acronym for "Put Your Data in Orbit"). In May 2018, Pydio switched from PHP to Go with the release of Pydio Cells. The PHP version reached end-of-life state on 31 December 2019.
Pydio Cells runs on any server supporting a recent Go version (Windows/Linux/macOS on the Intel architecture is directly supported; a fully-functional working ARM implementation is under active development).
The current offering of Pydio, known as Pydio Cells, has been developed from scratch using the Go programming language. Nevertheless, the web-based interface of Cells is very similar to the one from Pydio 8 (in PHP), and it successfully replicates most of the features, while adding a few more. There is also a new synchronisation client (also written in Go). The PHP version is being phased out as the company's focus is moving to Pydio Cells, with community feedback on the new features. According to the company, the switch to the new environment was made "to overcome inherent PHP limitations and provide you with a future-proof and modern solution for collaborating on documents".
From a technical point of view, Pydio differs from solutions such as Google Drive or Dropbox. Pydio is not based on a public cloud, the software indeed connects to the user's existing storages (SAN / Local FS, SAMBA / CIFS, (s)FTP, NFS, etc...) as well as to the existing user directories (LDAP / AD, SAML, Radius, Shibboleth...), which allows companies to keep their data inside their infrastructure, according to their data security policy and user rights management.
The software is built in a modular perspective; various plugins allow administrators to implement extra features.
Pydio is available either through a community distribution, or an Enterprise Distribution.
Features.
Client applications are available for all major desktop and mobile platforms.