The integration of Internet of Things (IoT) and Machine Learning (ML) technologies is revolutionizing how industries approach data-driven decision-making, automation, and resource optimization. This paper presents a detailed literature review of recent advancements in IoT routing protocols, ML-driven applications in healthcare and agriculture, and the role of smart systems in enhancing security, privacy, and wireless communication. By analyzing over thirty-five peer-reviewed articles, we offer a synthesized view of optimization algorithms, intelligent sensors, privacy-preserving frameworks, and dataset contributions that are driving the evolution of intelligent and scalable systems. The findings highlight key innovations, identify research gaps, and outline promising directions for future development in the rapidly expanding field of smart technologies.