There are so many threads here about these that readers are not really inclined to reply, I suppose.
Many members here have SBC's, I have seen it mentioned in various posts. It's nearly ten years since I acquired my first SBC.
The use cases are very variable. Typical things are:
- some kind of multimedia centre (standalone kodi on a minimal OS) for example libreELEC
- audio servers (Volumio, Pi MusicBox)
- multi-room synchronized audio (picoreplayer)
- NAS
- retro gaming (emulators of old console games etc) (https://retropie.org.uk)
- storage servers (you rent your hard drives in change of crpyptocurrency) (https://documentation.storj.io)
- DNS caching and ad locking (https://pi-hole.net)
- robotics and electronics projects, home automation
- CCTV type camera systems
The RPi is the most popular and perhaps the only "flaw" it has is that it cannot be booted without a closed-source proprietary blob. Well, you cannot boot linux anyway (you can do bare metal code). There is a project on github which was trying to create a open source booting firmware, but it is not production ready yet.
The RPi is the most reliable of these SBC's as there is a large team of staff and millions of volunteers using it. Other boards often have the problem that they require some patched kernel, customized OS or other idiosyncratic code to work, but the vendors are not so active (or might stop working on it entirely). This is one thing to keep in mind when thinking about getting an SBC - that you might be stuck on whatever software work on it now forever, if the support dies out and you don't have the time or required knowledge to do it yourself.
The old Pi's had some issues with the graphics side, 3D graphics and acceleration depended on experimental kernel modules. The latest version uses a new graphics chip and apparently you can run 3d games on it with relatively goof FPS (OpenGL ES 3.x on 500 mhz VideoCore VI)
There are other boards that have been around for long and have fairly good support. For example, Beagle board (they have some boards that can run full open source software stack even).
The place to hear about new ones is
http://linuxgizmos.com/