Abstract: Writing assistants are valuable tools that can help writers improve their writing skills. We introduce Effidit (\textbf{Eff}icient and \textbf{I}ntelligent E\textbf{dit}ing), a digital writing assistant that facilitates users to write higher-quality text more efficiently through the use of Artificial Intelligence (AI) and Natural Language Processing (NLP) technologies. We significantly expand the capacities of a writing assistant by providing functions in three modules: text completion, hint recommendation, and writing refinement. Based on the above efforts, Effidit can efficiently assist users in creating their own text. Effidit has been deployed to several Tencent products and publicly released at \url{https://effidit.qq.com/}.