One of the simplest methods of emulating stereo viewing also requires no special software to view or create: animated GIF. Most full-featured image editors can create animated GIF files from a set of images; some will automate the process more, but it’s simple enough to do manually without undue effort.
This works both with conventional stereo pairs and with multi-image like the Nimslo camera (intended for lenticular stereo prints). The images are pasted into an animated GIF file in a manner that causes them to display for a short time (.2 to .5 seconds per frame works well) in an order that seems to “tilt” the image right to left and back again. The GIF is then set to loop continuously, and any software that can display GIF (which is virtually everything that can view images) will show the image in a way your brain will interpret as 3D.
This works on phones, tablets, desktop or laptop computers, and even smart TVs — anything that can display a GIF.
Alternatively, for printed images, you may be able to train yourself to “free view”. This is a method of viewing stereo pairs without a viewer. It requires fooling your visual system into decoupling focus from convergence, to let you focus close while letting your eyes become parallel, as if viewing a distant object.
There are a number of tricks for this — the simplest is to hold the page with the image with something distant behind it. Look at the distant object, and move the page until the two images overlap (or ideally, fully fuse), then switch your gaze to the fused/overlapped images and let them come into focus without losing fusion. This is actually what a stereo viewer is doing, but the use of lenses makes it much easier.