Quba is a
e-Invoice-Viewer
Open-source / Free / Cross-Platform
Viewer for electronic invoices

We are Quba
Mustang's focusses on the creation, validation and parsing of electronic invoices. Validation also re-calculates important parts of these invoices. Quba covers the visual display for manual checks.
Quba 1.2.1
This version switches to the latest Mustangserver for invoice validation and updates Electron, allowing Quba to run on more recent Mac OS operating systems.
Quba 1.1.5
Version 1.1.5 of the open-source e-invoice-viewer Quba, released 2022-08-18, now also supports embedded invoice accompanying files >6MB.
Quba 1.1.2
Quba 1.1.2 has been released today, 11 November 2021, and adds support to drag&drop invoices onto the main screen.

Quba 0.5 with support for PDF and Factur-X/ZUGFeRD
With todays’ (2021-07-27) version 0.5 of Quba PDF-files can be opened. If the PDF file additionally contains embedded XML like Factur-X/ZUGFeRD-invoices do, a second tab
Quba 0.2 with UBL-support
Version 0.2 of Quba was released on 2021-06-10 synchronously for Windows, Mac and Linux. It features the support for UBL files, apart from UN/CEFACT CII
What about the name? Apart from being the name of a city in Azerbaijan, it also is the name of the horse breed originating from there. This name, like other horse names (Konic, Mustang) is a homage to the initiator of Factur-X / ZUGFeRD, the Forum of the Electronic Invoice Germany (“FeRD”, an accoustic allusion to the German word for horse).
Thank you for your support with the development of version 1.0
From now on community support and news are available via the ZUGFeRD Google Group.