Another one I like very much is how OS&#x2F;400 works.<p>Written originally in PL&#x2F;I and Assembly, it contains a kernel level JIT.<p>All user space applications target a general purpose abstract Assembly and they are AOT to native either at installation time or on-demand.<p>Other mainframes had similar approaches to code portability.<p>Sounds familiar?<p>Another cool thing are the catalog based filesystem and OO Assembly.