I have the Siltarp 2 for backpacking for a 2 person shelter. It's light, compact and is capable of covering a large area as a meeting place. It provides shade during sunny times and is a waterproof shelter for storms.
The Siltarp 3 is the big brother of tarps. It's capable of shading a picnic table and lives in my vehicle as an emergency shelter for occasional rainstorms. Six tent stakes and a hank of paracord are the best options for guying it out. Just make sure to try out a few configurations before you head out. This isn't your "take it out and set it up by following instructions" shelter. The Siltarp 3 is able to shelter 3 people in a rain proof shelter and weighs in at less than 2 pounds with the required accessories to make it functional.
It's well worth the investment. Don't settle for some box store blue tarp. Get one of these and stuff it in a tiny spot. You'll be thankful you have it when it's hot and sunny or cold and raining.
This review was written in the old system and had content requirements that are different than reviews written today.