Asynchronous online discussion environments are important platforms to support learning. Research suggests, however, threaded forums, one of the most popular asynchronous discussion environments, do not often foster productive online discussions naturally. This paper explores how certain properties of threaded forums have affected or constrained the quality of discussions, and argues that developing alternative discussion environments is highly needed to offer better support for asynchronous online communication. Using the Productive Online Discussion Model developed by Gao, Wang and Sun, we analyzed current work on four types of asynchronous discussion environments that have been developed and researched: constrained environments, visualized environments, anchored environments and combined environments. The paper has implications for developing future asynchronous online discussion environments. More specifically, future work should aim at (1) exploring new environments that support varied goals of learning, (2) integrating emerging technologies to address the constraints of current environments, (3) designing multifunctional environments to facilitate complex learning and (4) developing appropriate instructional activities and strategies for these environments. (Contains 1 table.)