Hi Taehyung,
ArchivesSpace and Archivists' Toolkit are two other open source applications for archival description, arrangement, and access. Archivist's Toolkit is no longer active - the core elements of the project were merged with yet another open source project, Archon, to create ArchivesSpace. More information on these applications can be found here:
While AtoM focuses on providing templates based on archival content standards such as ISAD(G), the ArchivesSpace editor's interface is more directly adapted from EAD - Archivist's Toolkit was originally often thought of as an EAD authoring tool, and elements of this approach have been carried forward into ArchivesSpace. Additionally, where AtoM combines description and access into a single interface, ArchivesSpace has a separate front and back end.
Further, while both applications are open source, each take very different approaches to maintaining and governing the respective applications.
You can read more about ArchivesSpace membership model here:
Archivematica (Artefactual's open source application for supporting digital preservation workflows) includes integration with both Archivists' Toolkit and ArchivesSpace for uploading DIP objects, though we do not maintain or develop these other applications.
Regards,