Zendesk Support Suite - Zendesk Support Suite is a tool that solves and emerges multiple tasks in one place.
Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.
Yet Another Mail Merge (YAMM) - Run well-targeted email campaigns with Gmail & Google Sheets
hiTask - HiTask is a free shared task list for your team. The place to plan, organize, and stay in sync.
Gmelius - Gmelius is the first collaboration platform designed for G Suite and your company's daily tools.
Mail Pilot - Beautiful task oriented email client for Mac, iPhone, & iPad