Genode comes with prebuilt USB live images that take the staggering amount of 20MB to download (see "Sculpt for The Curious", https://genode.org/download/sculpt) and supports running other OSes in VirtualBoxes.
The Genode OS Framework is a tool kit for building highly secure special-purpose operating systems. It scales from embedded systems with as little as 4 MB of memory to highly dynamic general-purpose workloads. Genode is based on a recursive system structure. Each program runs in a dedicated sandbox and gets granted only those access rights and resources that are needed for its specific purpose. [...] The framework provides mechanisms to let programs communicate with each other and trade their resources, but only in strictly-defined manners. Thanks to this rigid regime, the attack surface of security-critical functions can be reduced by orders of magnitude compared to contemporary operating systems. [...] In line with Unix philosophy, Genode is a collection of small building blocks, out of which sophisticated systems can be composed. But unlike Unix, those building blocks include not only applications but also all classical OS functionalities including kernels, device drivers, file systems, and protocol stacks.