FEN user guide
FEN tracks shared expenses for a trip, a flat or a weekend, and works out who owes whom.
What sets it apart is where the data lives: there is no FEN server. Expenses sit on your phone and, if you share them, in a storage account you provide. Everything that leaves the device is encrypted, readable only by your group.
One page per area of the app:
- Groups — creating groups, adding expenses, balances, settling up, closing.
- Friends — invites, your friends list, adding people to groups quickly.
- Settings — your profile, storage backend, additional devices, local backup.
- Backup & recovery — new phone, lost phone, and what comes back.
- Support — how to reach us: info@fenapp.net.
- Privacy policy — what FEN collects (and doesn't).
How FEN works
Your account is a key on your device
On first launch you type a name and FEN creates a cryptographic key. That key is your account: no email address, no password, no sign-in. Others see your name; the key is what identifies you.
This has one important consequence: nobody can reset your account for you. Lose the device with no backup and you lose the key, and with it the groups it could read. Backup & recovery is the five-minute setup that prevents that.
A group is a shared, encrypted history
A group is a log of everything that happened — expenses added, edited and deleted, settlements recorded, members joining and leaving. Every entry is signed by its author and encrypted with a key only members hold.
Your phone replays that log to get the balances. Every device replays the same log, so everyone lands on the same numbers with no server deciding anything.
Your storage backend carries the log
A shared log has to sit somewhere everyone can reach. FEN doesn't provide that — you point it at a Nextcloud instance you control, and whoever creates a group provides the storage for it. The operator only ever sees encrypted files.
Without a backend you can still join other people's groups and create your own local-only ones, which work fully on your device; you just can't share a group of your own until you add storage.
Sync happens when you ask
There is no push and no background server. FEN syncs when you open the app and when you pull down to refresh, so other members' changes appear on your next sync rather than instantly. That is the trade for having no server watching — pull down when you're waiting on someone.
Setting up the first time
The first launch walks you through three steps.
- Your name — what other members see. This also creates your account key. Already have a FEN account? Use Add device with backup file instead; see Backup & recovery.
- Local save folder — optional, strongly recommended. Pick a folder that syncs off this device (iCloud Drive, Nextcloud, Proton Drive, Dropbox) for your key backup and closed-group archives. Key backup switches on as soon as you pick one; add a folder password and both are encrypted.
- Storage backend — your Nextcloud details, or Skip for now. You need one only to create groups.
All three can be changed later in Settings.