The double wall tent is the traditional tent for many backpackers. There are some very light constructions to be found today. This is a Terra Nova Laser Photon 2009 weighing 775 grams in the above setup.
A tarptent is a tarp that has been turned into a single wall tent by adding a floor and some netting to keep the bugs out. This is one of my favourites, and still one of the lightest tarptents around, a Gossamer Gear The One 490 grams.
Halfway between a tarptent and a tarp? Mountain Laurel Trail Star at 650 grams including pegs is spacious but without floor or bug nets.
The tarp is the true minimalist shelter. Hendrik Morkel underneath his Gossamer Gear SpinnTwin that weighs 480 grams including poles and pegs.
Here I am in the rain, using the Terra Nova outer tent only. 550 grams including pole and pegs.
This shelter, which I made, is from Cuben fiber and very light. 165 grams for the fly and another hundred for the pegs, excluding bug bivy.
Here is one example of a homemade bug bivy that can be used under tarps. Weight 210 grams (7 oz).
Conclusions and current insights: The photos show some of the lightest solutions available. What strikes me is the small weight differences today between the lightest double wall tents and the lightest tarps and tarp tents. A tarp including some sort of bug net is really not that much lighter than a Terra Nova and often heavier than a Gossamer Gear The One.
For shelters used a lot above timberline, where the wind and the rain can be very intrusive, which is the case in Scandinavia, special care has to be taken. I would hesitate to use a true tarp for that (I could make an exception for a really big tarp); but I prefer something that can be pinned down to the ground all around and has a low profile with small surfaces of fabric for the wind to grab. Like, for instance, the Terra Nova Laser. Right now light pyramid shelters are popular. I am a bit hesitant of these since they tend to have quite large fabric areas for the wind to press against. That is my experience from using similar (but heavier) tents some decades ago. But since people like Andrew Skurka have used them for looping Alaska I imagine they work well enough even in exposed tundra country.
For shelters used a lot above timberline, where the wind and the rain can be very intrusive, which is the case in Scandinavia, special care has to be taken. I would hesitate to use a true tarp for that (I could make an exception for a really big tarp); but I prefer something that can be pinned down to the ground all around and has a low profile with small surfaces of fabric for the wind to grab. Like, for instance, the Terra Nova Laser. Right now light pyramid shelters are popular. I am a bit hesitant of these since they tend to have quite large fabric areas for the wind to press against. That is my experience from using similar (but heavier) tents some decades ago. But since people like Andrew Skurka have used them for looping Alaska I imagine they work well enough even in exposed tundra country.
Shelters made from Cuben fiber are now becoming commercially available even from larger manufacturers. I think they will become more common in the next few years. Awfully expensive, though.