Add a Balance Forward (account summary) area to Invoices
To clarify what this is, here is an image:
Because our templates are HTML, and many are customizing heavily, we don't have an easy way to enable this with a checkbox or anything quite that simple.
For now, you can copy a short HTML snippet into your template and swap out the balance_due tags for a new tag called {{customer_open_balance}} that reflects the total of all open invoices.
You can find those snippets here:
https://gist.github.com/theinventor/c1a0b866e4ed8962f434
If you want an entire invoice template to see where these fit, here you go:
https://gist.github.com/theinventor/d0546d11ede2a2cd9b2d
To add these just head to Admin -> Invoice Template -> Edit
Click the <html> button to view the source of the template, and scroll down to where you see the first instance of this:
<div class="invbody">
^That is the line items table, so insert this new snippet on the line right above that.
If yours comes out looking wrong, you can reset your template, or go back to any recent version.
Enjoy!