Lifehacker covers it, almost the entire internet knows about it, but I still found the idea of a moss terrarium quite appealing. It means that I can have at least some greenery in my room, without the requirement that I keep my blinds open for sunlight or stay on top of watering it regularly (Succulents are also good for this, but I've already had those for a number of years). It's not shown in any of the pictures, but I capped the mason jar to try and keep the humidity higher, and keep the maintenance requirement lower.
Picnic Day. If I had it to do again, I'd make sure to put some rocks under the dirt, and I'd have made sure the jar was really clean before I started. Small neck terrariums like this are an uphill battle against keeping the glass clean, so starting with anything less just makes your job harder later.