Download the Day Planner 0.11 source code.
Extract the package with the command
tar -jxvf ./dayplanner-0.11.tar.bz2. The source code is now extracted to ./dayplanner-0.11/.
To run Day Planner run the command
./dayplanner from the directory dayplanner-0.11. Read the INSTALL file for installation instructions.
You may also want to look at the Day Planner git repository.
The MD5 sum of the tarball is 34c3bfb39e4dd1bc89384bdfb46c4169