Most blocks can slide horizontally as well as vertically.
If not, an arrow on the block will indicate the limited sliding liberty.
A few blocks are not allowed to move at all. They are part of the canvas.

I have added the minimum amount of moves and actions needed to solve a puzzle.

On the applets, you could let 1 block push other blocks too, but if you move 4 blocks at once, it is counted as 4 moves and counted as 1 action. 
About the difficulty:

1 -> Basic
2 -> Challenging for beginners, rather easy for more experienced players.
3 -> Great challenge for beginners, not so hard for more experienced players.
4 -> Pretty hard
5 -> Very hard
6 -> Seemingly impossible

I have not given a difficulty rating to many of the mazes because it is too hard to compare different mazes in difficulty.

And last, but not least, many thanks to Mr. Pierre-François Culand for this wonderful applet. The existence of this site depends on it.

This site is best viewed under a resolution of 1024x768 or higher.
I compiled these puzzles under java 1.5.0. If your browser can't handle this, you could update your java here by downloading the JRE package.

D= Difficulty
M= minimum of Moves to solve it

-> if the number is written in green, the solution to the puzzle was provided by Bob Henderson.
-> if the number is written in red, the solution to the puzzle was provided by Daniel Blazewicz.
-> puzzles with a * have no proven shortest solution but a short solution has been found

A= minimum of Actions to solve it