Franzis sells a lot of software -- franzis[.]de/ . Their Projects line is a portion that they've been expanding, in part by selling software that's not developed in-house, though honestly there's little way to know if past Projects apps are the work of contractors. To keep up with the competition much of their newer software uses AI, while the lack of updates for some of their older Projects apps *might* indicate they're on their way to being retired. FOCUS projects *may* fit into that category, and understandably since it's always been more of a niche product, as photo stacking has always been a bit of a niche itself.
You use software like FOCUS projects for focus stacking, a technique that means combining 2 or more [often Many more] shots, each focused a little bit further away from the camera. If this sounds too tedious, and difficult given the lack of manual focusing controls on many cameras, there are gadgets you mount your camera to, then turn a knob to move it incrementally forward/back, with some pros using an automated motorized version. The basic hardware is inexpensive -- you can find the individual parts on eBay [or similar] and assemble the setup yourself. To use it once the camera's focused you 1st lock the focus, then turn the knob, take a shot, & repeat.
Why would you use photo stacking? You've probably heard of, & I know you've seen a photographic effect called bokeh, where the subject is in focus but the background is blurred. While it's often achieved in software, it's also an effect of the lens settings, where you have varying Depth of Field, meaning how far into the distance things remain in focus. Bokeh is very popular & common in Macro [Extreme closeup] photography, because attention is purposely directed to the subject, e.g., flower, insect etc., being photographed. When this bokeh is achieved by the lens settings in a macro photo, the depth of field can be Extremely shallow, with only a single flower petal being in focus for example. Often that's just what the photographer is after, but if not, if they want the entire flower or insect or whatever to be sharply in focus, they can use photo stacking.
My personal opinion is that adding bokeh in software nowadays is so easy & the results so good that achieving it with the lens settings in macro photography isn't as necessary as it once was. You'll get sharper results stacking, but you might not feel the added sharpness is worth the effort, &/or you might prefer a degree of softness. Some photographers do use stacking for landscape and architectural photos, usually using [far] fewer shots to make up their composition.
digital-photography-school[.]com/a-beginners-guide-to-focus-stacking/
wikipedia[.]org/wiki/Focus_stacking
georgedouvos[.]com/focus-stacking-in-landscape-and-architectural-photography.html