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.
17hats - The all-in-one business system for entrepreneurs.
Notion - All-in-one workspace. One tool for your whole team. Write, plan, and get organized.
Bill.com - Bill.com provides ACH payments processing, automates your accounts payable and accounts receivable processes.
Slack - A messaging app for teams who see through the Earth!
Zoho Invoice - 100% free online invoicing software for small businesses.