It's just insane that Arc Forum doesn't encrypt HTTP but, well, as you write, we can't change Arc Forum. Maybe they'll update it some day, or someone will set up an unofficial one that's more up to date?
It looks quite humble but it has both a repl and an interface for saving/running various web apps.
I've set it to be enabled by default in Anarki. And it's only available for admins, because it can run system commands. I wonder if it would be possible to allow any user to develop apps securely, e.g. by disabling unsafe commands or sandboxing it somehow? Perhaps there is a simple way of doing that? It could open Arc web app development up to any user of an Anarki driven page.
I think those features mentioned above still need better documentation, too.
Other HN features that Anarki News is lacking:
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* past front pages
* show all stories from same site by clicking on domain name