Syncthing is fantastic, and is mostly private. With a little effort, you can make it completely private by setting up your own discovery and relay server (though the docs on how to do that could really be improved).

If you want to try nextcloud use the nextcloudpi project. It takes care of everything you need to set it up.

I use seafile. The docs are so so, the support is not great but the product did not failed once for two years (with my server being on linux (docker) , clients on linux, windows and android)

If you are looking for a commercial (not opensource) self-hosted dropbox alternative, FileCloud (https://www.getfilecloud.com) is great. It comes with great support and has clients for windows, mac and linux.

Full Disclosure: I work here.

I have been a very happy user of Syncthing over Wireguard (connecting all my devices back home). Adding to that a VM of "OpenMediaVault" for NAS/Backup, PiHole to catch what Ublock misses, and music streaming via FunkWhale, I have managed to host a good majority of my own data.

Is there anything that has a client for Linux, Mac, and iOS? Not just a website, but a dedicated app.

NextCloud has desktop clients and mobile apps: https://nextcloud.com/install/#install-clients . ownCloud has them too: https://owncloud.com/download/#desktop-clients

A Synology NAS + Synology Drive has replaced Dropbox for me. Drive isn’t quite as polished, but I have effectively unlimited space, and it’s more private.

This also turned out to be a good alternative for me, although I kept Dropbox and had my Synology backing up everything to it so clients use Drive to sync to NAS then NAS to Dropbox.

Then my NAS died very prematurely, rather than buy another proprietary piece of hardware from Synology I muddled through setting up DSM in VirtualBox on a more powerful machine with xpenology. Using their operating system in a virtual machine lets you use their mobile apps too, about the only thing you can't do is use their QuickConnect service but there are other dynamic-dns services you can use in its place.

https://xpenology.com/forum/topic/13834-virtualbox-dsm-62-ds...

Also love my Synology NAS. I can connect my external services to it (Dropbox, Box, etc.) and wire those in as well. They make it painless and super trivial.

What about not fully Dropbox alternatives, but simple solutions to have a backup of files online and sync those files with different computers?

Unison works well. https://www.cis.upenn.edu/~bcpierce/unison/

rsync is incredible efficient and reliable. I use Nextcloud for some things. But it is just too slow for large data (Gigabytes and tens of thousands of files). Especially it they change frequently. HTTP and webdav is slow and the clients are not reliable. Last week I tried to transfer 20000 photos (for Mapillary) from a phone using Nextcloud. It took forever and the Nextcloud app crashed after a few hundred photos. Rsync (syncopoli on the phone) worked like a charm and did the job in no time.

Plus it is just so convenient using SSH because you can easily make tunnels and still have end-to-end encryption.

Large sized files are not a problem with Nextcloud. Large amounts of files in a single directory are. A .git dir in nextcloud will trash performance.... but my photo library is perfectly performant :shrug:

For those of us that have the same aversion to setting up an entire web server for a simple browser-based access to their files as I have, I recommend also having a look at https://filebrowser.xyz

I have an instance running at home (reachable only via VPN) that simultaneously syncs the files via Syncthing, and the combination of the two is surprisingly effective.

Adding to this this project currently in beta, a simple self-hosted private Dropbox with E2EE: https://www.duple.io/en/