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

I've been using it for years and it's all good.