At CurrySoftware GmbH we use ledger + recutils + aqbanking + custom bash scripts to automate many business processes.

Some of these processes are required by german law and many companys outsource these to accountants or tax advisors or buy shitty software from DATEV.

The great advantage in staying fully plaintext is, that you do not need to automate everything for the whole system to work. Incoming invoices are frequent -> write a bash script, Outgoing invoices are frequent -> write a bash script. Paying the state back some VAT happens once a month, use emacs to do it manually. I really love it.