Is there a free, actively developed IRC client for Snow Leopard?
Try Adium, which has IRC support and a lot more all free and its still under active development. Also it supports Snow Leopard on the current 1.5.3 version, as long as your up to at least OS X 10.6.8.


  Supported services
  
  
  XMPP ("Jabber"), including
  
  
  Google Talk
  LJ (LiveJournal) Talk
  Facebook Chat
  Gizmo5
  
  MSN Messenger
  AOL Instant Messenger (AIM), including
  
  
  MobileMe (formerly known as .Mac)
  
  Yahoo! Messenger, including
  
  
  Yahoo! Japan Messenger
  
  ICQ
  Bonjour, compatible with iChat
  Twitter
  IRC
  MySpaceIM
  Gadu-Gadu
  IBM Lotus Sametime
  Novell GroupWise