Syncthing provides a similar capability to proprietary systems such as Dropbox, and also is well suited for use with low power single board computers. You can have one or more directories which are synchronized across your various laptops/desktops/devices, and this makes it hard for you to ever lose important files. The manner in which the synchronization is done is pretty secure, such that it would be difficult for passive adversaries (mass surveillance, "men in the middle", etc) to know what files you're sharing. Of course, you don't necessarily need to be running a server in order to use Syncthing, but if you do have a server which is always running then there's always at least one place to synchronize your files to or from.
Freedombone provides Syncthing shared directories for each user on the system, plus a single shared directory for all users. The expected most common scenario here is that of a family in which members may not want to share all of their files with each other, but might want to share some in a common pool (eg. birthday photos). You can also easily share between different servers.
On a laptop
Install syncthing on a Debian based distro:
curl -s https://syncthing.net/release-key.txt | sudo apt-key add - echo "deb http://apt.syncthing.net/ syncthing release" | sudo tee /etc/apt/sources.list.d/syncthing.list sudo apt-get update sudo apt-get install syncthing
Or on Arch/Parabola:
sudo pacman -S syncthing
Add syncthing to your startup applications, so that it begins running when your system starts. Then either restart your system or run the command "syncthing" from a terminal.
In another terminal log into Freedombone:
ssh username@domainname -p 2222
Then select File Synchronization.
Select Show device ID and copy the long string of letters and numbers shown, using the shift key then select the text followed by right click then select copy.
Open a non-Tor browser and enter http://127.0.0.1:8384 as the URL. You should now see the minimalistic user interface. Under Remote Devices select Add Remote Device. In the Device ID field paste the string you just copied (CTRL+v). The Device name can be anything. Under Share Folders with Device check default (or whatever folder you created on your local machine), then save.
From the top menu select Actions and then Show ID, then copy the ID string (usually select then CTRL+c). Go back to the terminal control panel menu and select Add an ID then paste what you just copied (CTRL+v). Optionally you can also provide a description so that you later can know what that string corresponds to.
Now wait for a few minutes. Eventually you will see two messages appear within the browser asking if you want to add two new folders from the Freedombone server. Say yes to both, and specify ~/Sync as the directory with your username and ~/SyncShared as the shared directory. You can now copy files into your ~/Sync directory and they will automatically be synced to the server. Those will be files which only you can access. If you copy files into ~/SyncShared then they will also be available to any other users on the system.
Install Syncthing and Connectbot from F-droid.
Set up Connectbot to log into Freedombone.
Select File Synchronization.
Select Show device ID and copy the long string of letters by pressing anywhere on the screen, selecting the menu then copy and then selecting the ID string. This is very tricky on a small screen, so expect to fail multiple times before you succeed in copying the text.
Open Syncthing and select the devices tab. Press on + and then paste the device ID with a long press followed by Paste. You may need to remove any stray characters which were copied during the previous haphazard selection process. Add a name, which can be anything.
Now select the menu (top left or menu button) and then press on Device ID. It will be copied to the clipboard. Go back to Connectbot and from the control panel select File Synchronization followed by Add an ID. You can then paste in the ID with a long press, and optionally add a description for the device. When that's done you can disconnect from Connectbot.
Now wait for a few minutes or more. Eventually you should receive two notifications (swipe down from the top to see them) which will allow you to confirm the connection to the server. Say yes to both, and specify appropriate directories for your files and the shared files. To reduce battery and data usage via the settings you can also set Syncthing to only sync while it's charging and only while it's connected to wifi.