Copyright law (and therefore DRM, the software companies can use to lock down their products) in the US is controlled by the Library of Congress. Every three years, the Librarian makes decisions on certain critical exemptions. This time around, it looks like they have got things right.
The rules specifically cover Section 1201 of the Digital Millennium Copyright Act, which governs fair-use exemptions from all sorts of things. You might be familiar with DRM from MP3s and movies, but it's far wider-reaching.
Yesterday's exemptions allow people to legally access the software in their cars, to repair or tinker; jailbreak their smartphones; run multiplayer services for old, out-of-support video games; and rip DVDs to make fair-use remixes.
These are all completely sensible and reasonable exemptions, so it's almost sad that we have to celebrate them. But given the current broke-arse state of DRM and copyright management, we'll take any small victory.