Originally and still used as an agricultural tool today. You can buy both straight blade and curved bladed versions in markets in Thailand, Cambodia, Laos, etc. They are quite effective for clearing underbrush as you will see in the video. Kind of like a beefier and modified version of a sickle. :-) SEA Billhook.
https://www.youtube.com/watch?v=dCSsEFLpi5Q