Deftere Yaz: Shop Credit Book

Deftere Yaz is the shop's credit book and customer ledger (the veresiye defteri of Turkish corner shops) on your phone. A regular says "put it on my tab"; you write the amount and the balance adds up by itself. Who took what, who paid what and how much you are owed, on one page.

LIKE THE PAPER BOOK, WITHOUT THE ARITHMETIC
• Add a customer, tap "Write credit" or "Take payment", type the amount. A note and a date are optional.
• Every customer's balance, and the balance after each entry, line by line as in the book.
• A customer who has paid everything is crossed out; a settled account gets a stamp.
• What is owed in all, today's credit and today's payments on the first page.
• Bring over an old balance from the paper book when you add a customer.
• Take back or correct a wrong entry; the balance is worked out again every time.

ONE BOOK FOR THE WHOLE SHOP
• Your staff join with the shop's six-character code and write in the same book from their own phones.
• Every entry shows who wrote it. Change the code to take someone out of the book.
• No accounts, no emails, no passwords.

REMINDERS AND STATEMENTS
• Send a polite reminder over WhatsApp to a customer who owes; you word the message for your shop.
• Share a PDF statement with every entry and the balance.
• A reminder on the 1st and 15th of the month: who owes how much.

REPORTS
• Sort by balance, by name or by the last visit; search for a customer.
• A summary page: this month's credit and payments, the last seven days, the largest balances and the longest-unpaid customers.
• Export every customer and entry as CSV for a spreadsheet.
• A home screen widget with what is owed and today's entries.
• Keeps working offline and syncs when you are back online.

Amounts are in Turkish lira. Deftere Yaz is free, with ads. Customer details belong to your shop and are stored on servers in the European Union; the last phone to leave a book deletes it.