TvOS

tvOS is the Operating System that is used by the Apple TV 4G. It's a stripped down version of iOS. The first version released was stylized and marketed as tvOS 9.0, which was based on iOS 9.1. Since then, tvOS versions trail those of iOS by 0.1 (i.e. tvOS 9.1 is based on iOS 9.2, etc).

Research
As demonstrated in http://newosxbook.com/articles/OTA.html?n, Apple provides a complete OTA image of TvOS, which enables one to reconstruct the entire system partition along with all binaries, in order to perform static analysis on them.

Additionally, Apple has not actually fixed any bugs from Pangu's iOS 9.0.x Jailbreak in 9.1 but the kernel exploit (CVE-2015-6974), the Pangu9 jailbreak could be used with some modifications (notably, a different kernel bug) in order to achieve a tvOS 9.0 jailbreak. Note that the same could not be said for tvOS 9.1 and later, as iOS 9.2 (from which 9.1 is derived) has patched many vulnerabilities.

An overview analysis of tvOS can be found in http://newosxbook.com/articles/OTA3.html.