This paper details architecture, mathematical modeling, and use cases of a new distribution system power flow analysis tool (called DxFlow). The DxFlow is developed in MATLAB environment and is made completely open source. Thefirst version of DxFlow can solve single-phase and poly-phase power flow analyses using standard forward-backward sweep (FBS) method. Moreover, DxFlow allows easy integration with heuristic optimization algorithms for solving optimal settings of equipment on distribution level (such as load tap changers and capacitor banks). DxFlow also allows time-series power flow analysis. Themathematical model in DxFlow is validated using the IEEE test feeders, compared with OpenDSS and GridLAB-D models, and additional new cases are presented to demonstrate its usefulness. The DxFlow is primarily intended for educational and early-stage research purposes.