I have talked previously about free CAD editors and one of the big winners was DesignSpark Mechanical 2, where FreeCad was close. These two software packages are very good but also very different. DS Mechanical 2 is a direct modeller and FreeCad isn’t (yet). Basically DS Mechanical 2 works like moulding clay where you push and pull surfaces. On the other hand FreeCad requires a sketch, dimensions defining the sketch, and everything is linked together through actions history. These are real editing softwares and require installation and are heavy…. But if you just want to see a STEP file or a IGES file?
You can use LSTC LSPP. It’s available in all the major flavours (including MAC).
Here is an example: