GPU Caps Viewer is a free, portable graphics card information tool with a strong focus on developer-level OpenGL, OpenCL and CUDA-related details.
The program's GPU tab has useful hardware details which will appeal to any knowledgeable user, though: your GPU model, memory size and type, BIOS version, current temperature, fan speed and clock rates, voltages, driver details and more.
But then life begins to get rather more complex. So you can view your OpenGL version, for instance; low-level CUDA details like warp and grid sizes, block dimensions and more; and an OpenCL report detailing the drive version, global and local memory amounts, samplers, OpenCL extensions and more.
And you even get a Shader Validation option where the program will check the compilation of any type of GLSL shader - vertex, pixel (or fragment), geometry, tessellation control and evaluation - to make sure that all is well.
There's just about enough useful options here for the program to be appealing to regular users, though, too. If you're having problems running OpenGL or OpenCL software, for instance, then GPU Caps Viewer includes a few demos you can use to test your setup. There's no need to understand the low-level technical details, just choose a demo from the list and watch to see if it works (or not).
GPU Caps Viewer provides a host of low-level data regarding your graphics card(s). It's targeted at developers, but may also appeal to expert users: if you've overclocked your card, say, the program will help you monitor how it's doing.