My single greatest gardening discovery is the sickle, which in fact folks around here have used since prehistoric times. I bought my sickle about 10 years ago, after noticing that all the village women carried one when they headed out to their fields and gardens. My elderly neighbor taught me how to use it and keep it sharp, and it's been my faithful gardening companion ever since: it's the one tool I always have with me when I'm out in the garden (I already posted about this ancient tool here).
The sickle is one-handed tool with a wooden handle and a long curved blade that is primarily used to cut grass, but can be used in weeding and to cut other vegetation, even brambles and small branches. The curved blade is handy for gathering up whatever you've cut and carrying it away in bundles, while its point is useful for digging out tough roots.
The most efficient way to use a sickle is simply to slice through the vegetation with a one-handed stroke, but I've never quite mastered that, so I typically hold the vegetation at the top with my left hand (shielded for safety by a leather work glove), while swinging the sickle with my right hand.
This weekend, I used it to clear the back wall of our new garden plot, which had been overgrown by ivy that was also invading the terrace. The sickle goes hand in hand with a sharpening stone: the sharper the blade, the easier the cutting. To cut ivy, which is relatively woody, I needed to sharpen my sickle quite frequently as I worked.
It took me about 20 minutes to cut the ivy back to an acceptable level. I don't plan to remove it completely, though: my aim isn't to destroy the natural landscape with my gardening. Using a sickle instead of a power tool allows me to cut selectively, preserving a healthy relationship between garden and nature.