Albert is 100% free and the #1 Invoicing App in the UK, Winner of the Orange Award (Best Startup in the UK) and featured by the App Store twice while I worked there, once more since then. 

Invoices & expenses dramatically simplified: No more shoeboxes or lost receipts. Keep all your invoices and expenses together in your pocket. Creating them is easy as sending a picture with Whatsapp.

The finance app you hardly need to use: Night or day Albert will make sure you automatically know about the important things happening to your invoices and expenses. No need for you to keep tracking anymore.