Siel_Acumulus

The Acumulus addon connects your Magento store to the Dutch SIEL Acumulus online financial administration application. It can add your invoices automatically or via a batch send form to your administration, saving you a lot of manual, error prone work.

So, the Acumulus addon assumes that:

You have an account with SIEL Acumulus (see https://www.siel.nl/acumulus/ or https://www.siel.nl/acumulus/koppelingen/webwinkels/Magento/).

If not, this addon is useless and will not do anything.

The Acumulus addon:

Reacts to order status changes via events.
Does have 2 admin screens: a settings and a batch send screen.
Does not in any way interfere with the front-end UI.