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Quip: Team Documents for Slack - Create, share and get notified about Quip docs in Slack

DEVONthink - DEVONtechnologies develops DEVONthink, DEVONagent, and other Mac and iOS apps for document and information management and web research.

Trainual + Slack Integration - Capture knowledge or access training right inside Slack

TaskSurfer - TaskSurfer gives you all of the tools you need to manage things the way you want.

Papermind - Papermind Slack App is a collaborative article-editing and document management platform for Slack