If you want to compare them I would suggest to have a look at Tizen:Common and Mer ...

At least both projects cooperate to same upstream packages ...

Samsung is also funding and developing EFL inside the Linux community and they've been doing that for years now. Plus, Tizen isn't even Samsung's baby, it's a Linux baby which Samsung contributes to (maybe a bit more than others, but still not their OS).

At least from what I've seen, things never went really well. I think there was some toolkit-level (Silica <-> Ubuntu API) wishes for collaboration, but nothing happened there at all, due to lack of time from the Jolla side in my opinion - although I was not surprised to see that not pan out honestly, given the endings of similar past efforts for cross-platform API compatibility even with teams in the same company (Symbian <-> MeeGo) also having trouble.

I would have expected to have seen more collaboration on layers below the UI, libraries, daemons, and such, but Ubuntu seem to pretty consistently have decided to do things Their Own Way, and ignoring most of Jolla's (and formerly, Nokia's) open source work on contacts/calendaring, sync, telephony, and all sorts of other areas. And then there's the more public differences (like Mir instead of Wayland).

I won't publically speculate about why they do this, but honestly, all I can see it doing is harming, and continuing to harm them. Their choices - for whatever reason they are made - are affecting their ability to ship products. One day, maybe they'll realise that.

In terms of cooperation between Tizen and Sailfish, I don't see it as something that is realistically possible without either a lot of pain or a lot of compromise on one end or another. MeeGo was a pretty good case study in that, if you were following the technical details (there was a lot of pain and politics in which components were to be used, and which were to be thrown to the side), and the end result was quite lacking in some areas, considering it was supposed to be post-1.0 in terms of version numbering.

I also don't see it as being something that necessarily really benefits either side. I mean, changing software and distro tooling, inducing communication overhead, differing QA/integration/etc structures, etc, etc - all for what? Sharing a bunch of software packaging? I don't see the benefit, frankly.

"Sailfish OS" to me has always been about integrating a bunch of open source software projects, writing a few new ones to fill the gaps, dropping a UI on top of it - and doing all necessary integration/QA/testing gruntwork to make a consumer product out of the disparate pieces. The 'real' software work is supposed to happen outside of the distro projects themselves (in Sailfish's terms, that's Mer, Qt, etc projects).