I like to collect old sewing machines, looking in antique stores and thrift stores for ones to work on. Mostly I like treadles and smaller machines. I get amazed at the simple mechanics of these machines.
If you know how to sew, then you know that most domestic sewing machines use the same system of a spool of thread for the top thread and a wound bobbin for the bottom thread. If you have to do alot of sewing you know how quickly the bobbin thread can run out and has to be rewound.
The National company made a sewing machine, The Two Spool, in the early years of the sewing machine industry that in my opinion was the best of ideas; instead of having a bobbin, it used a full spool of thread for the bottom thread. The spool of thread rested in a barrel shaped area under the bed of the machine and interacted with the needle to make the stitch the same way that a bobbin did. I think that is a fantastic idea and wonder why that design, that technology died in favor of the bobbin that is common now.
I saw one of these Nationals in an antique shop, it was a treadle, and wanted so much to buy it, but sadly didn't have the money. It was in beautiful shape. Whoever does buy it I'm sure they will enjoy using it.