Here is a frameless 52 liter Golite Jam2 pack that I used for a 3-week 500 kilometer trek. The photo shows it with food for 8 days, and total packweight is between 13-14 kilos (29-31 lbs).
This homemade pack weighs a scanty 300 grams (11 oz) and holds 8 kilos (18 lbs) for a 13 year-old on his way to one week of backpacking in high alpine country, sleeping outside in a tarptent.
This is a 685 gram (24 oz) pack with a "frame" consisting of some carbon fiber struts. It is a ULA Ohm and I like it for slightly heavier loads, like here with a packraft and paddles. Intial total packweight for this trip was 16 kilos (35 lbs) with food for six days.
This Mariposa Plus from Gossamer Gear is similar to the ULA Ohm, with a stabilising "frame" and weighing around 685 grams (24 oz). In the photo is is also loaded with food for six days as well as packraft and paddles and weighing 16 kilos (35 lbs).
Comments and new insights
For loads up to 13-14 kilos (29-31 lbs) I find that packs that has no internal support or frame at all works better than you would think. But most people used to sturdy packs weighing 3-4 kilos (7-9 lbs) will probably have some psychological difficulties in switching to something completely frameless. Since there are packs weighing less than one kilo (2.2 lbs) that has some sort of frame and will carry everything a smart backpacker will need, that is what I would recommend. Examples of packs like this, that I have used myself, are ULA Ohm and Gossamer Gear Mariposa Plus. Lots more on this important subject in the book.