Really, it's just a tab strip, no? (But with fixed heterogeneous tabs, as oppose...

Really, it's just a tab strip, no? (But with fixed heterogeneous tabs, as opposed to a set of homogeneous ones the user adds/removes from as they open/close docs.)

Reminds me of the vertical tab strips in FF w/ TreeStyleTabs.

Which reminds me of OS/2, where tab strips were on the side, with some nice skeuomorphism: https://www.landley.net/history/mirror/os2/history/os221/vxr...