i3-gaps
A fork of the i3 window manager with gaps and some other features
...Gaps come in two flavors, inner and outer gaps wherein inner gaps are those between two adjacent containers (or a container and an edge) and outer gaps are an additional spacing along the screen edges. Gaps can be configured in your config either globally or per workspace, and can additionally be changed during runtime using commands (e.g., through i3-msg). Outer gaps are added to the inner gaps, i.e., the gaps between a screen edge and a container will be the sum of outer and inner gaps.