General construction kit for real world applications. In theory you could take a machine apart and use the beams for some other machine. A smaller kit could build any of the machine designs as needed.
The problem with grid-beam is that it really only seems to make sense if you A) have lots of grid-beams in various sizes already, and B) are making, taking apart, and repurposing things frequently. Without A, making grid beams is a lot more work than just purpose-cutting your pieces, and without B, you don't really have a reason to drill all those extra holes.
The grid beam book talks a lot about what you need to make beams from scratch. You don't have to do that. You can buy (or print!) beams and get to work right away.
[1]: https://twitter.com/hugs/status/707381021646323712
[2]: https://www.mcmaster.com/8809T7-8809T21/
[3]: https://bitbeam.org/
I've been working to document everything I've done with Gridbeam, and related tech here: https://wiki.replimat.org/wiki/Main_Page
I lived with Phil and RJ Jergenson for a couple years around 2012, tried to learn from their experience and mistakes. They weren't happy with 1ft lengths in every project, even though they were an improvement in reusability over all lengths free-for-all. I've since moved all the replimat designs to use lengths 2, 3, 4, 5, 10, 15, 20, 25, and 30 only. Which allows for center pivots and divisible-by-two lengths whereas the Jergensons could only divide by two. We also hit countertop height a little better. Little tweaks.
I try to communicate with everyone listed in the "Friends" section on the right hand side of https://www.replimat.org/ regularly. I'm excited that things seem to be gathering steam for all of us.