ShellMate is an open-source command line productivity tool powered by OpenAI. It accepts standard input, command line parameters, and highlighted text as prompts, aiding users in quickly recalling commands and predicting upcoming command needs. With the highlighting feature, users can concentrate without needing to ask questions. Additionally, users can directly ask questions and insert AI-generated suggestions in the terminal using the 'sm' shortcut, eliminating the need to leave the terminal interface.