In recent years, smart contract technology has garnered significant attention due to its ability to address trust issues that traditional technologies have long struggled with. However, like any evolving technology, smart contracts are not immune to vulnerabilities, and some remain underexplored, often eluding detection by existing vulnerability assessment tools. In this article, we have performed a systematic literature review of all the scientific research and papers conducted between 2016 and 2021. The main objective of this work is to identify what vulnerabilities and smart contract technologies have not been well studied. In addition, we list all the datasets used by previous researchers that can help researchers in building more efficient machine-learning models in the future. In addition, comparisons are drawn among the smart contract analysis tools by considering various features. Finally, various future directions are also discussed in the field of smart contracts that can help researchers to set the direction for future research in this domain.