Structurizr Lite
This free and open source version of Structurizr allows you to view/edit diagrams, view documentation, and view architecture decision records defined in a single DSL or JSON workspace. Structurizr Lite can be used standalone for workspace viewing/authoring, or in conjunction with the cloud service/on-premises installation as an authoring/testing/staging environment.
Please note that Structurizr Lite is only designed to be used by a single person, and has no collaboration features built-in. Having multiple people concurrently access the same Structurizr Lite instance, or running multiple Structurizr Lite instances concurrently against the same folder may result in unexpected behaviour (workspace content corrupted, diagram layout lost, etc). The on-premises installation or cloud service are recommended if you require team/collaboration features.