All of the mods you can find on this page which are all made by me are now open sourced.
If you want to take a look at the code for the Peacefulpack, Goblins and Giants, Harder Peaceful etc. you can now do that over here.
All of the code is licensed under the GNU GPL license which pretty much means, use it in any way you want, just don’t copy it over and release it somewhere else.
One thing you should now about the code is that some of it may look very bad. That is because a part of the code that is online is over a year old and made before I even knew Java. There is also outdated code which I haven’t fully updated to 1.6 yet and there is other code I am working on right now which may also not work fully. So learn what you want from the code, but like almost anything it is not perfect.