**5. Conclusions**

In this paper, we have discussed the existence and multiplicity of positive solutions for a system of Riemann–Liouville fractional differential equations with singular nonnegative nonlinearities and *p*-Laplacian operators, complemented with nonlocal boundary conditions involving fractional derivatives and Riemann–Stieltjes integrals. Some properties of the associated Green functions are also presented. Two examples are constructed for the illustration of the obtained results.

**Author Contributions:** Conceptualization, R.L.; Formal analysis, A.A., R.L. and B.A.; Funding acquisition, A.A.; Methodology, A.A., R.L. and B.A. All authors have read and agreed to the published version of the manuscript.

**Funding:** The Deanship of Scientific Research (DSR) at King Abdulaziz University, Jeddah, Saudi Arabia funded this project, under gran<sup>t</sup> no. FP-18-42.

**Acknowledgments:** The Deanship of Scientific Research (DSR) at King Abdulaziz University, Jeddah, Saudi Arabia funded this project, under gran<sup>t</sup> no. FP-18-42. The authors thank the reviewers for their constructive remarks on our work.

**Conflicts of Interest:** The authors declare no conflict of interest.
