Today I tried with the newest nightly build and I got: dab:~ jdabel$ cd /Developer/Examples/Ruby/MacRuby/HotCocoa/graphics dab:graphics jdabel$ macruby particle.rb Segmentation fault dab:graphics jdabel$ macruby demo.rb 2009-12-03 17:03:51.063 macruby[153:903] *** -[NSLock unlock]: lock (<NSLock: 0x2004855c0> '(null)') unlocked when not locked 2009-12-03 17:03:51.065 macruby[153:903] *** Break on _NSLockError() to debug. /Library/Frameworks/MacRuby.framework/Versions/0.5/usr/lib/ruby/1.9.0/hotcocoa/mappings/application.rb:9:in `handle_block:': undefined method `on_action' for 0:NSSlider (NoMethodError) from core:in `application:' from demo.rb:1:in `<main>' dab:graphics jdabel$ My Mac: Modellname: MacBook Modell-Identifizierung: MacBook5,1 Prozessortyp: Intel Core 2 Duo Prozessorgeschwindigkeit: 2,4 GHz Anzahl der Prozessoren: 1 Gesamtzahl der Kerne: 2 L2-Cache: 3 MB Speicher: 4 GB I would choose MacRuby for Hotcocoa!!! Juergen Dabel Schrobenhausen Germany