Simple arches from two trees pulled over and tied at the top are fantastic – they will graft together eventually. You could plant a series of pairs of apples (or pears) like this along a central vegetable garden path. To create this I would get two parallel metal arches and put them a metre or so apart, with horizontal metal bars connecting them at around 300mm spacings. Planting an apple (a young bare-rooted maiden two years old or so) with a rootstock such as M106 either side would allow you to bend the tree, as the wood would not have hardened up too much. You could then take side shoots out to follow along your horizontal bars to form a curved espalier for your path.