MeisterTask is a collaborative to-do list app for team and project managers / members.
Pro Useful integrations
MeisterTask has integrations with Google Drive, Dropbox, Slack, GitHub, BitBucket, Zendesk, Zapier, and MindMeister. You can even get a personal URL to subscribe to your tasks, schedule, etc. via any calendar program that supports the iCal format (e.g. MacOS default calendar application, or maybe even Fantastical 2 on the same platform).