There are several document management systems (DMS) that can be used on Debian and Android and can be synchronized using Syncthing. Here are some options:

1. Paperless-ngx:
   1. Description: Paperless-ngx is an open-source document management system that offers OCR functionality and can extract metadata from documents. It can be synchronized with Syncthing by setting up a shared folder where documents are uploaded and automatically processed.
   2. Usage with Syncthing: Users can set up a Syncthing folder where documents are uploaded, and Paperless-ngx can automatically process these documents and extract metadata.
   3. Platforms: Available for Debian and Android.
   4. Source: Reddit Discussion.
2. Mayan EDMS:
   1. Description: Mayan EDMS is another open-source document management system that offers extensive features for managing documents and metadata.
   2. Usage with Syncthing: Similar to Paperless-ngx, Mayan EDMS can be configured to process documents from a Syncthing folder.
   3. Platforms: Available for Debian and Android.
   4. Source: Reddit Discussion.
3. LetoDMS:
   1. Description: LetoDMS is an open-source document management system based on PHP and MySQL. It supports document metadata, version control, and automated email notifications.
   2. Usage with Syncthing: LetoDMS can be configured to process documents from a Syncthing folder and manage metadata.
   3. Platforms: Available for Debian and Android.
   4. Source: Medevel Article.
4. ProjectSend:
   1. Description: ProjectSend is a secure, simple, and powerful open-source file-sharing system. It supports multiple languages and has a responsive design that works on various screen sizes.
   2. Usage with Syncthing: ProjectSend can be configured to manage files from a Syncthing folder and synchronize metadata.
   3. Platforms: Available for Debian and Android.
   4. Source: Medevel Article.

These systems can be synchronized with Syncthing by setting up shared folders that are monitored and processed by the DMS. Syncthing itself supports the synchronization of metadata and can be used on various platforms, including Debian and Android.