Quip: Team Documents for Slack - Create, share and get notified about Quip docs in Slack
Dialog Messenger - handy and feature-rich enterprise multi-device messenger available for server or cloud – Slack-like, but not Slack-limited
Trainual + Slack Integration - Capture knowledge or access training right inside Slack
Ripcord - A desktop chat client for Discord and Slack
WorkStudio - Simple, collaborative work management
Ziggs - Smoothly Share Content Between Devices!