There are some alternative firmware projects like samygo (for Samsung) and openlgtv (for LG):

https://wiki.samygo.tv/index.php5?title=Main_Page

http://openlgtv.org.ru/wiki/index.php/Main_Page

But they support AFAIK only a limited number of devices and also only some firmware versions (it seems like both Samsung and LG are attempting to close the doors).