I’ve long recommended Nextcloud as a wonderful open-source, private Infrastructure-as-a-Service (IaaS) cloud. I run it myself both on a server in my office and on my TMDHosting remote server. Over time, though, Nextcloud has been adding more features. These include built-in video-conferencing and group meeting services. Nextcloud Talk and Software-as-a-Service (SaaS) version of the LibreOffice office suite, Collabora. Now, with Nextcloud 20, other third-party services such as Microsoft Teams, Slack, Jira, GitHub, Twitter, and dozens of others are being integrated.
