I need to build a small HMI application that will communicate with several PLCs via Modbus TCP. I also want an option for multiple Web clients.
I'm looking for a simple and cheap HMI software for this application, (Software like Cimplicity, WinCC, etc... are too expensive).
What are the requirements for the HMI? Do you mainly need the web clients or do you do you need some sort of touch screen HMI?
Mango Automation https://infiniteautomation.com/data-visualization/ is an inexpensive software application that runs on Windows and Linux. It does really well with Modbus TCP and has a pretty advanced Web HMI builder that makes super nice screens. All the HMI screens are HTML based so work really well in browsers and mobile devices, but if you want a local HMI you'll need to use a tablet or something to display the web pages from Mango.
I've not used them yet (clients usually ask for AB), but I've heard good things about Maple Systems. Their hardware is certainly cheaper than the competition. I'm not sure about the software, but if it costs anything at all I'm sure its comparatively less.
I've also used a lot of Proface. Not free, but not expensive either, cheaper than most. It seems they broke their way into the scene on price point. haven't used them in a few years so I can't guarantee they're still cheap. Look into it.