Logic number puzzle: Kakkuru.
Download Kakkuru desktop application (Windows 64bit)  Download Kakkuru source code (Lazarus/Free Pascal) 
Description: Puzzle game with numbers to be placed onto a grid. The rules of the game are as follows:
1. In the white grid fields, write numbers from 1 to N (N = number of white fields in a row/column).
2. In each row and each column, each number must be written exactly once.
3. The numbers in the black fields are the sums of the numbers in the white neighborfields.
The game is a typical logic game: In order to find the correct solution of the puzzle, you have to explore the sums given and numbers already written, and by logical
thinking (concluding from what you know, that a given field must be a given number, or on the contrary, can't be a given number), determine, which fields have to
contain which numbers.
The game is played with the mouse: Click the field, where you want to write a number, then click one of the number buttons to write the corresponding number or Clear to remove the number from the actually selected field.
Change log.  

Improvement: The generation of 6x6 fields puzzles sometimes takes several seconds. Changing the corr. algorithm would improve game
comfort...
Free Pascal features: Changing the color of shapes and the caption of statictexts during runtime. Using buttons to insert characters
into a given control's caption. Twodimensional arrays (classic Pascal).
Screenshot: