Made iMovie on Mac - how do I convert it to .avi

How do convert this file (I think iMovie files are .mov) to a .avi - with a free converter?

You may try isquint. It’s totally free, but I’m not sure if it could convert video to avi.

If you would convert video frequently on Mac, I recommend you an all-in-on mac video converter.
Key Features.
1. Convert various format video(MOV/MP4/FLV/AVI/WMV/MPEG...) to each other.
2. Support HD video.
3. Customize video specs.
4. Video editing function, including crop black bar on screen, trim time length for a specific video clip, merge several video clips into a single file etc.
5.Support batch conversion and merging video clips into one file.

WMV Video Converter for mac, DVD to WMV Ripper.

I am afraid iSquint can not convert .MOV to AVI. You can try some free online converter.
http://zamzar.com/
But it can not convert big files.
You can also use this video converter for mac. It can convert .MOV to AVI on Mac with high quality.