Femlisp can make use of the 2D mesh generator Triangle by J. R. Shewchuk and the 3D mesh generator Tetgen by Hang Si.
On Debian/GNU Linux, these programs can be installed using
sudo apt install triangle-bin tetgen
When this succeeds, the corresponding binaries “triangle” and “tetgen” should be found, and can also be used by FEMLISP.
Note that for a lot of model problems, the mesh can be constructed in a rather straightforward way, such that mesh generators are not needed. Especially, this is the case for most of the FEMLISP demos.