postix is an open source cashdesk software that was written for Chaos events and has been used at MRMCD16 and 33C3.
It features a simple and clean frontend for the cashdesk that allows a high throughput (there were no queues to speak of at the ~12k person event that is 33C3). It has a pretix import, and supports a variety of ticket restrictions, such as by warning message, by a provided code (e.g. a membership ID), or making some tickets only available at certain times (e.g. late-night tickets or day passes). Additionally, it has two separate frontends:
The cash accounting frontend is for the process of giving out cash and goodies to a cashier and receiving them back afterwards. It validates the appropriate amounts, prints reports, and can also export data.
The other frontend is for people supporting the cashiers. It shows when goodies run low, or when a cashier requests assistance. It can also be used to print tracking codes to determine the wait time in the queue.
postix has shown to be a stable and mature system even though its development happened in under a year on spare time.