5G technology has been designed with flexibility and software reusability in mind. In this context, open-source developments are critical enablers for mastering software architecture and associated codes, which are of the utmost importance for all technology stakeholders (ranging from manufacturers to operators and service users). free5GRAN is a new open-source 5G development framework. It focuses on research and education. It provides a modular architecture and a set of well-documented APIs, which enable easy experiment reproduction. free5GRAN aims at easing the understanding of 5G standards and the development of new technology components. The global objective is to be as modular as GnuRadio project [1], but with full system implementation. It has not been designed with performances in mind, unlike other open-source projects such as srsLTE [2] and OpenAirInterface [3]. The current release implements a significant part of the PHY layer on the receiver side, and the MAC layer will be part of a future release. Its architecture, which is composed of a library and an implementation part, is described. Moreover, RAN components are explained, and custom implementation methods are provided. It has been tested and validated against a commercial Amarisoft 5G SA gNodeB in a Faraday Cage.