Recently I bought a second hand Nikon EM. I found that these analog cameras used a very neat trick to focus. After some googling I found that this is called the "focusing screen".
Do focusing screens still exist in digital cameras or is it possible to mount them in a modern DSLR? I can imagine that it's really usefull when manual focusing.
What you are showing isn't just a focusing screen. It is a focusing screen with two special focusing aids. First, it has a split prism, which works as a tiny rangefinder — when the two sides are aligned, the subject is in focus. Second, outside of that, the rough microprism ring gives a similar effect, with a different tradeoff between ease of focus and actually seeing your subject.
The whole thing, even without these special features, is the focusing screen, and every SLR has one, digital or not. The image from the lens is projected onto this and that's what you see through the viewfinder. (This is in fact the whole trick of the SLR design. The mirror positions have screen at the same effective distance as the film or sensor, so what is in focus on one will be in focus on the other.)
However, with the advent of autofocus, the focus aids are no longer common — and further, the screens are usually optimized to be brighter, at some expense in being able to discern focus manually.
Some high-end DSLRs are still made where this is an easily replaced part, but screens with these aids aren't generally an option for DSLRs — except for from third parties. And fortunately, you are in luck there, because there are a number of options, including the company (no longer operating) Katz Eye and several Chinese sellers who operate through eBay. These will sell you a part you can install yourself, with different options sized for most DSLRs. (Depending on the model you have, they'll be easier or harder to install yourself.) You can get versions with various aids, including split prisms aligned in different ways, or just with different etched guidelines.
Note that there may be some drawbacks — a darker screen, impeded autofocus, and possibly shifts in metering — as the camera wasn't designed for this. These vary by screen and by camera. If you manually focus most of the time, it may be worth it.
Simple answer: yes. Inexpensive option: 'Bresson'. Here's a review. I have one for my 5100.
