Are http://meta.stackexchange.com/ and http://careeroverflow.com/ part of the SE ecosystem? I definitely think Career Overflow isn't but better to confirm. And if they are, they (both) don't offer an option to connect other SE accounts.
What is meta?
- Any Stack Exchange user can ask a question
- The community provides support, votes on ideas, and reports bugs
- Your voice helps shape the way Stack Exchange operates
Meta Stack Exchange was the meta for the original Stack Exchange 1.0 system. If you look at the bottom for the contact address, you'll notice it's email@example.com. So it is part of our system, just somewhat defunct since SE1.0 is being phased out. There has been some back-and-forth about merging it with this Meta.
CareerOverflow has a contact address of firstname.lastname@example.org, and is copyright careeroverflow.com at the bottom instead of "Stack Overflow Internet Services Inc.". It's likely they are one of the Stack Exchange 1.0 sites, which are not owned by Stack Overflow.