[nine_k]

For PHP, there is HVVM which, AFAICT, can run vanilla PHP and is open.

TruffleRuby is a thing, as is JRuby.

Implementing Erlang without implementing its VM and the whole infrastructure, which is a much larger task than merely a VM like Python's.

[Shish2k]

HHVM dropped vanilla-PHP compatibility after PHP7 started coming close to it in performance (which was the top reason anyone used HHVM to serve vanilla-PHP code) - now they’re focussing on Hacklang which, no longer shackled by the need to be bug-compatible with PHP’s awful design decisions, is free to become a better language