Another recommendation for your reading list: The Plan 9 kernel (could be considered a modernized version of a classic code reading which is also highly recommended: Lions' UNIX 6th Edition commentary).
The Go compilers and stdlib are also a great read. Is no coincidence that Ken Thompson was involved in all those projects.
More on topic: I agree it is sad how underrated Tcl is, perhaps not the best language ever created, but deserves much more attention and credit than the latest JS-flavour-of-the-week.
Tk is also great and IMHO still the best portable GUI toolkit around.
Tk is great. What I don't get is why people are still making applications that don't use ttk and it's modern theme. It's Motif look on linux is the single biggest complaint I hear about it today and that problem was solved what, a decade ago?
As an aside, LTK, which is basically just lisp bindings for talking over a socket to wish is the only lisp gui that I've had work on all platforms and all lisp implementations.
I don't have a proper list, it is more in the back of my head. I did read some of these each:
* Erlang VM
* sqlite
* Linux kernel
* Clojure functional data structures
That list may look very pretentious, but I don't try to fully understand the packages. What interests me is (1) the style, and (2) the larger strokes. What kind of idioms are there, and how does it fit together. I think it is pretty hard to get the idea of a software package from reading the code. For that some higher level description or book makes more sense. Generally I think reading source code is very helpful in becoming a better programmer. I don't think the above list is anywhere near a general recommendation. I did rather pick a domain that was intimidating to me, and the reduce ignorance there.
