Nextcloud 9

As it says, "The self-hosted alternative to Dropbox". If you have a server with sufficient resources, you can use this great self-hosted solution that handle a lot of things via plugins. It handles tasks, desks, calendars, files handling, mails and so on...

It works, but you can break it, if you are a poweruser or mishandling it

It combines lots of cloud features in one simple UI. And it can be self hosted..

One of the best open source projects of the decade. If you don't want to or cannot self host, /e/ foundation provides a hosted version which includes a free tier: https://e.foundation/ecloud/ If you're new to self hosting, Linode provides an easy one-click app and you can get the first couple of months free: https://www.linode.com/marketplace/apps/linode/nextcloud/