Many requirements engineering tools have been existing for gathering, documenting and tracing requirements that can even be further processed for such purposes as analysis and transformation. In this study, we analysed 56 different requirements engineering tools for a comprehensive set of features that are categorised into multiple viewpoints (i.e., project management, specification, collaboration, customisation, interoperability, methodology, knowledge management). The analysis results led to many interesting findings. Some of them are as follows: (i) the project planning and execution activities are rarely supported, (ii) multi-user access and versioning are highly supported, (iii) the top-popular specification technique is natural languages, while precise specification via modeling languages is rarely supported, (iv) requirements analysis is rarely supported, (v) requirements transformation is considered for generating documents only, (vi) tool customisation via the tool integration and API support is highly popular, while customising the notation set is rarely supported, (vii) exchanging requirements is popular in such standards as ReqIF and Excel/CSV, while no single standard are accepted by all the tools, (viii agile development is very common, while other methodologies (e.g., MDE and SPLE) are rarely supported, and (viii) user-guide, telephone, e-mail, videos are the top methods for sharing knowledge. The analysis results will be useful for different stakeholders including practitioners, tool vendors and researchers.