KWVR uses an EPOS (Electronic Point of Sale) system by Merac - can't tell you more because I only sell things using it.
The KWVR system is technically called "MStore" by a company called K3 Business Technologies. It was originally designed by a small company called Merac for leisure attractions, but Merac got sold to K3 some years ago when the original owner and designer retired.
Like any IT system it is not perfect, nothing ever is, but is generally good at what it does.
For the KWVR it is an integrated system that we use for online ticket sales, booking office ticket sales, in shops and tea rooms, and also for the membership system. All are integrated allowing quite a bit of flexibility in what you do and how you do it.
It's a bit clunky in the background to set things up as over the years lots of new features have been bolted on to it for different users. But once you get used to it it's quite easy.
With bookings you can assign seating plans and coach layouts to bookable services, allowing the user to choose their own seats, or you can choose to allocate seats yourself.
The system is used by a number of heritage railways in various different forms. Kent and East Sussex, Mid Hants, NYMR, and Swanage all spring to mind as some of them.
Like lots of things it is what you make it. The great benefit we have found at the KWVR is the ability to have everything integrated across all locations, all methods of selling and all our systems such as membership, sales, catering, booking offices and online all using the same system. Even the on train bar and ticket inspectors use it in a smaller more mobile till form, which generally works ok. They will work offline, but do need connection to the internet to do certain functions, which is why we have fitted routers and wifi to our bar cars to allow connection on board.