Molden
Molden is a visualisation software for QM calculations.
The home page is https://www3.cmbi.umcn.nl/molden/.
The current version is 5.8
The program can be downloaded by anonymous ftp from
ftp ftp.cmbi.umcn.nl
cd pub/molgraph/molden
A precompiled version for Ubuntu Linux is avaliable in
cd pub/molgraph/molden/bin/Linux
It worked well 2021.
You can build molecules by the Z-mat editor (primitive, but working)
Click on add Line
Select the element
Click on the atom to which it should bind, another to form an angle
and a third to form a dihedral.