Quip: Team Documents for Slack - Create, share and get notified about Quip docs in Slack
HoudahSpot - Advanced File Search Utility for Mac OS X
Trainual + Slack Integration - Capture knowledge or access training right inside Slack
Yojimbo - Yojimbo makes keeping all the small (or even large) bits of information that pour in every day...
WorkStudio - Simple, collaborative work management
DEVONthink - DEVONtechnologies develops DEVONthink, DEVONagent, and other Mac and iOS apps for document and information management and web research.