(warning: Requires a somewhat-sketchy-seeming-but-harmless-i-think Java applet. Chrome gives you a hard time about it, but if you create an exception for the site in the java control panel (on OS X: settings->Java->security), then you can play it in Safari)
http://pot.home.xs4all.nl/infocom/
I highly recommend Planetfall.
(warning: Requires a somewhat-sketchy-seeming-but-harmless-i-think Java applet. Chrome gives you a hard time about it, but if you create an exception for the site in the java control panel (on OS X: settings->Java->security), then you can play it in Safari)