Bulker builds multi-container computing environments that are both modular and interactive. A bulker environment consists of an individual container image for each command. Bulker environments are portable, interactive, and independent of any specific workflow. Bulker simplifies both interactive analysis and workflow development by building drop-in replacements to command-line tools that act like native tools, but run in containers. Think of bulker as a lightweight wrapper for docker/singularity to simplify sharing complete, containerized environments.