Ceel, maybe it's an old topic, but I'd like to comment, as I'm also interested in WM topic and tried them out (see my previous post few days ago):
-openbox doesn't really freeze after login with SLIM, it just uses SLIM background for wallpaper for some reason. If you click the desktop with your right mouse button you will see the OB menu. Yes a bit confusing I also guessed first the login failed... If you want to change the wallpaper you probably need to install nytrogen or feh package. Or see if can change it with PCmanFM or rox-filer as they should have a function in menu for managing desktop background.
-for other WMs agree with you, if I recall correctly, some don't work, some would start if logged in as root account, some are too ancient noone would use except under justx.
-You may also try starting them from within running lxde or openbox session by for example $killall openbox; awsome
New topic, we'd need some newer FMs where development is going on:
1) Windowmaker 0.95.8 released a year ago (http://windowmaker.org/). I tried compiling it with toolchain and slitaz-dev-pkgs (./configure && make && make install). There were just few Dev packages missed, which I installed. Process took 5 minutes and was flawless. I was impressed by this version. Very nice, light and working well, installed some new good looking theme downloaded online. Great look and feel!
2) FVWM 2.6.7 released end 2016 (http://www.fvwm.org/). Compiled no problem same as above. Looks great even without installing additional themes like fvwm-crystal, fvwm-nightshade or fvwm-themes. Started from running openbox or lxde session $killall openbox; fvwm2
3) Afterstep 2.2.12 released 2013 (http://afterstep.org/). Similar look to Windowmaker, probably more difficult to configure, haven't tried compiling yet, but it seems not having many dependencies, would definitely work.
4) CDE Unix is now open source, 2.2.4 version some end of 2016. Haven't tried compiling.
All these 3 WMs look like a gois, clean, lightweight, recent up-to-date alternative WM. Would give it a shot. Windowmaker is probably the better choice, or Fvwm. You cannot just convert them from .Deb or .rpm or txz, I tried different even few years older versions from Ubuntu, Debian, slack or void, in most cases it fails on the old or different glibc version used in slitaz, or libpng, ...
Now, for my own usage this traditional compilation is ok. But would be great if someone experienced with slitaz packages cooking would make tazpkg normal way, which I am not versed in, and put it in the repos. Also, I assume to have all the functions (which I don't need personally, but others may), may need to add langues support say for German and french and Russian at least. I could not see the title of a Chinese website on Windowmaker for example...
Just ideas... Anybody of same interest?