I think Tizen lets you write your own apps. I know I installed Emby on one of the very cheap smart tvs recently and had to install it via developer mode and pull in the package by typing the IP of my laptop into the TV (maybe vice versa).

I didn't write the code but it seemed like you can get a development account from Tizen and write your own apps.

To be clear, Tizen is not a brand of TV, it's the name of the OS. It's fairly common on various no-name hardware brand, check it out.