diff --git a/docs/principia/Principia.nw b/docs/principia/Principia.nw
index f6fd624e..fbe5ead4 100644
--- a/docs/principia/Principia.nw
+++ b/docs/principia/Principia.nw
@@ -3,6 +3,10 @@
 % recent links:
 %  - https://github.com/oasislinux/oasis minimal-oriented linux distro,
 %    with lots of simpler variants of big libs (e.g., musl not glibc)
+%  - https://github.com/danistefanovic/build-your-own-x
+%  - https://github.com/mit-pdos/xv6-riscv
+% - https://aquadzn.github.io/learn-x-by-doing-y/ lots of cool tutorial
+%   on how to build zip from scratch, HN clone, etc.
 %  - https://c9x.me/ mini editor, yacc, C compiler, etc.
 %  - http://nandgame.com/ WEBUI following nand-2-tetris but gamified a bit
 %  - https://web.eecs.utk.edu/~azh/blog/challengingprojects.html
diff --git a/profilers/Profiler.nw b/profilers/Profiler.nw
index 85bdbe87..7381c80d 100644
--- a/profilers/Profiler.nw
+++ b/profilers/Profiler.nw
@@ -1,5 +1,8 @@
 \documentclass[12pt]{report}
 
+%last:
+% - https://www.markhansen.co.nz/profilerpedia/
+
 %******************************************************************************
 % Prelude
 %******************************************************************************
diff --git a/shells/Shell.nw b/shells/Shell.nw
index ff22fb88..66ad9866 100644
--- a/shells/Shell.nw
+++ b/shells/Shell.nw
@@ -7,6 +7,10 @@
 % - https://elv.sh/
 % - https://www.oilshell.org/
 % - https://www.micahlerner.com/2021/07/14/unix-shell-programming-the-next-50-years.html
+% https://github.com/oilshell/oil/wiki/Alternative-Shells
+% choc programming language shell (see pdf in principa-project/Shells/)
+
+% https://angelhof.github.io/files/papers/shell-2021-hotos.pdf
 
 \input{../docs/latex/Packages}
 \input{../docs/latex/Config}