There's the NumWorks calculator with its emphasis on modern UI/UX and their source code is available on GitHub, but it's not open-source and they recently had t

There's the NumWorks calculator with its emphasis on modern UI/UX and their source code is available on GitHub, but it's not open-source and they recently had to lock things down because of issues with some particularly obtuse national exam boards in Europe about the openness of their platform... Otherwise there's also Casio with the Graph-3E+E II and the Graph-90+E (European models, I'm not familiar with the American ones) and HP with the HP Prime, but they all run proprietary firmwares. There's also SwissMicros with their DM42 calculator where they recently split and open-sourced their Free42-based application from their proprietary operating system for GPL licensing reasons. But they target the engineering market and they don't have Press-To-Test capability. There are competitors out there and the graphical calculator market situation is far healthier in Europe than North America. But to break TI's monopoly over there you'd need to somehow break their T³ (Teachers Teaching with Technology) lobbyist program and their hold on teacher unions, textbooks and politics...