It's developed with the support of the Linux Foundation, with the code released under open source licences. There are some parts of the design that are licenced by Samsung (e.g the SDK), but overall it looks pretty open to me.
>"it's not a real platform"
It has shipped in multiple devices, including every TV Samsung have sold since 2015:
https://wiki.tizen.org/wiki/Devices
>"It's a toy Samsung uses to threaten Google with."
It's a little more than that. At the moment it's not got much traction on phones, but I still maintain it's the best option for an open-source mobile OS that we've got left now that Ubuntu are out of the picture. If you can think of a better alternative that currently exists, by all means feel free to share it.
Some core components are not (or were not) free software. And the license for the SDK gives Samsung the rights to revoke forbid specific users from using it.