These saws are very useful if you need to transport a saw for work away from your workshop. Some are small enough to be carried in the side pocket of cargo pants, and all are good for protecting the blade when carried in a toolbox with other tools.
Z-Saw make several such saws as follows:
These saws have Teflon-coated blades for rust resistance, and can be locked in any position between fully open and fully closed. They are available in 3 sizes - 210, 240 and 270mm blade lengths - but all 3 have identical tooth patterns.
These have quality aluminium handles with a rubberised coating for grip, and are really excellent saws for toolboxes. They come in 2 lengths, 210 and 240 mm, and a choice of finer or coarser blades in each size.
Both of these are fairly new products but already very popular. The VIII 265 carpentry saw (a video here shows this saw in use) and the V handy folding saw shown below are both Group D saws and therefore interchangeable with a wide range of blades and handles (although a long 265mm blade would not be well protected in a handle made for a 200mm blade, and the reverse might look a little silly).