My favourite X11 window manager for many years was tvtwm. Eventually I moved on to gnome (JDS) and then XFCE, but largely because they had workarounds for some of the more errant clients that seem to be common rather than any weaknesses in tvtwm itself.
I recently tried to make piewm work, and it didn't. The problem seemed to be inside the lex parser, and I didn't want to dig too deep there. It ended up being easier porting the pie menu support to the current (pl11) version of tvtwm, so that's what ptvtwm is.
My source code is available. This just builds a copy of tvtwm with pie menu support.
Some of the code is a bit clunky, and there are bugs. I did this largely to see what piewm actually did, and learnt a little X along the way.
I've built it for Solaris and made the packages available. These packages deliver both tvtwm and piewm from the ptvtwm source, and a private copy of xli as xloadimage used by tvtwm/piewm to load the desktop background. The packages also include two related twm derivatives - ctwm and vtwm.
Choose the right file from the following list:
To install,
pkgadd -d PCTtwmplus.i386.pkg PCTtwmplus
where you should replace "PCTtwmplus.i386.pkg" with whichever file you downloaded.
(Using pkgadd should work on OpenSolaris distributions too. You can safely ignore any conflicts marked as "attribute change only". And binary compatibility should ensure that the software works correctly as well.)