Sitecake - Drag and drop CMS for HTML websites. It's flat file CMS so it's pretty fast.
Airtable - Airtable works like a spreadsheet but gives you the power of a database to organize anything. Sign up for free.
Anchor CMS - Free and lightweight blogging system
Creativity 365 - Cross-device content creation suite
Textpattern - Textpattern is an elegant content management system that is free, open source software.
Microsoft Teams - Microsoft Teams provides the enterprise-level security, compliance and management features you expect from Office 365, including broad support for compliance standards, and eDiscovery and legal hold for channels, chats, and files.