In terms of limitation... Construct Free Edition. The engine in itself isn't bad, it's the limitations.
There's also the VX Ace lite, which is free. For a good example of what can be accomplished with even that much limitation-look at Dreaming Mary. The art is superb, though watch out for the horror. Not for the faint of heart. Don't be fooled by the pastel pinks!
Pixel Maker MV. That's the worst. Bad UI, bad translation of the UI elements, unclear and limited options. It's glitchy a bit. Honestly, you shouldn't buy it just to produce kusoge (crap game.)