The correct answer is 'Online workspace'. An online workspace is designed to facilitate collaborative work in real time, and includes features such as simultaneous document editing, real-time feedback, and tracking version history, making it the most fitting option for the team's needs. 'Email client' is primarily for sending and receiving emails, which is not optimal for real-time collaboration and simultaneous document editing. 'Conferencing software' is mainly for virtual meetings and does not offer comprehensive document editing or versioning features. 'Instant messaging software' is designed for direct messaging and may lack the advanced document collaboration capabilities the team requires.