I consider July 15 the deadline for planting kale, turnips, broccoli, etc so it will get big enough before frost to make it through the winter. I sowed Bok Choy around July 15 last year and it made nice heads in the fall, probably the most successful Bok Choy I ever grew; maybe it would still perform now. I think the bush beans I sowed at the same time didn't have time to make beans. Maybe really short season greens would do fine, or transplants. When it starts getting colder toward fall it really slows down the growth of vegetables.

Any leafy greens--kales, mustards, arugula, lettuces, spinach, mache--will do well at this time of year. I'm trying sprouting broccoli for the first time this year; planted them about a week ago. Sprouting broccoli is a biennial so it needs to winter over and then begins producing in April. Some folks have luck with a late pea crop, but I've never been able to get them to produce. It's not just the cold either, it's the short days.