Avoid VirtualBox and becoming trapped in the non-free & personal use only extension by using one of the very decent open source alternatives Boxes[1] or virt-manager[2]

I do not understand, Virtual Box is free software, the versions distributed through most common Linux distributions does not contain any non-free components and the binaries on the site are released under the GPLv2. The extensions you mention are a separate download that you explicitly have to download and it is mentioned around the download that they are under a different license.

How exactly are you trapped by using GPL software?

NullPrefix

Without the extension VirtualBox VMs are pretty much shit.

rbanffy

For tools like Vagrant, not at all. They are very useful if you want to attach USB devices directly to the VM, use the built-in webcam and so on, but I've used VirtualBox for years without installing the extension once.

torstenvl

USB 2.0 and 3.0 are not fully supported without the extension pack.

koolba

Which again are irrelevant for the common “just for Vagrant” use case.

rbanffy

I have used it for testing on different Windows browsers, to check whether https://github.com/rbanffy/3270font would install correctly, and running some Windows software from my bank. The only time I needed the extensions was when I needed to reflash my Blackberry 10 DevAlpha (whose battery, sadly, is dead - I loved that phone)