Diary App for Mac OS X (equivalent to Chronories)
Don't know exactly what features of Chronories you use the most and would like to find in another tool but here are two possibilities.


MacJournal
Mémoires


Both work on Leopard and its snowy friend.



edit following question's clarification:  

With low requirements and going for free solutions, you could simply go to EverNote. You'll have as a bonus the possibility to sync your notes from everywhere, including mobile devices.
You have the possibility to order your notes by date, which would then mimics a diary. It's far less sexy than the above solutions but could fulfill your requirements.



second edit
A new one I saw today on the Mac App Store:  


Day One


Seems quite nice, low price and good feedback until now.