TryC is for writing and running small C program. It's just for C learners.
Mac OS X includes Developer Tools a developing environment for making Macintosh applications. But if someone wants to study programming using C, Xcode is too big and too complicated to write a small sample program for beginners. TryC is just for such kind of "beginners".
You don't need to launch huge a Xcode application or type unfamiliar commands in Terminal using TryC you can write, compile and run C program just like TextEdit. It's only available to compile one source code file but it's enough for trying sample programs.
I hope you enjoy studying C and step up to Cocoa someday.
Mac OS X 10.4 PPC
Mac OS X 10.4 Intel
Mac OS X 10.3.9
||MacOSX10.3 or later ( Intel Mac available ) and DeveloperTools