JSesh is used and supported by the IFAO 
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JSesh 2.13.3 doesn't run on Mac OS X tiger
Submitted by Serge Rosmorduc on Thu, 11/19/2009 - 14:50.
solved:
solvedI have accidentally used features of java 1.6 in the latest version of JSesh. Mac OS X tiger (and of course leopard) doesn't support this version of Java. I will fix it, but let's say that it's a bit difficult to remain polite considering Apple's policy for java version. Java 1.5 could still be installed on Windows 98... Java 1.6 can't run on a two years-old Mac.
Temporary Workaround:
Send a letter to Apple about their Java upgrade policy. Wait a little, I'll fix it. Meanwhile, install an older version of JSesh.