[MuffinFlavored]

https://en.wikipedia.org/wiki/Linux_kernel_version_history

I wonder if there is a sizable position easily identifiable Linux 2.6.x running out there.

[Lammy]

Lots of old Androids https://android.stackexchange.com/questions/51651/which-andr...

[dezgeg]

Plenty of routers (especially on Broadcom chipset).

[doodlesdev]

There probably are a lot of NAS all around the world still running that version, probably somewhat patched with some backporting though.