In this paper, we present a novel 5G NR simulator aligned with Release 15 TS 38.300. The work relies on previous implementations of LTE and mmWave modules. The focus of the paper is on the MAC layer, where we present the refactoring and the improvements to support OFDMA as per standard. A novel, user-friendly and modular interface is also proposed for the scheduler part, that allows a symbol-level distribution of resources. We go through the details of the implementation, and then we present scheduler results for a subset of schedulers that we propose. The code is available for interested users.