You will get many dozen recommendations. What have you tried or found thus far?
A few of us here are fans of OpenSCAD, but it's not for everyone.
Fusion 360 (free hobbyist version) is also popular, as is OnShape.
For the most basic of programs, Tinkercad, free, web-based can do many things.
For organic (curves, bumps, roundy-round stuff) there's Meshmixer. On the challenging side, Blender.

Stay away from SketchUp, as it creates non-manifold objects more often than not.

There are others.

I can confirm that the mushroom lady file is no longer available.