The game now has an online multiplayer mode! You can invite anyone from your friends list to join your game. Just click the bird and select a friend from the invite dialog. Your friend can then accept the invite from the chat window. That's it - then you should be playing together on the same board.
Previously there was only Steam's Remote Play Together, which can be a bad experience if the internet connection isn't good enough. The new true online multiplayer mode is much simpler to use and independent of the quality of connection.
There is also a new achievement that is earned by inviting someone to your game.

Although the rules of the game are quite simple, it may be hard for beginners to understand certain core tactics. Which is why now, while your mouse hovers over a point of the board, the game will display comments such as "Risky", "Suboptimal" or "Invalid". This should help with learning to play the game. Comments are only displayed in the lowest difficulty mode (the Fly), but not in higher levels and also not in multiplayer.

• "Risky" means that the stone you are about to place is easily and quickly captured by the opponent. Not only the most obvious cases are detected, but rather tricky ones too.
  
• "Suboptimal" means that there are better options nearby to place your stone.
  
• "Invalid" just means that the move is against the rules. The game won't let you make that move.

Please note that there is no absolute guarantee that the program classifies all situations correctly. There could always be special cases that I didn't think of. I'd be glad if you share screenshots of incorrectly classified situations with me, so I can fix them.

• It is no longer necessary to manually start the computer player after each move when the game is in tree stump mode. Instead you only need to start it once and the game will remember to automatically start the same computer player after you make a move. You can still interrupt it by clicking on the cross and then select another difficulty level at any time.
  
• Fixed a visual glitch where button animations didn't play correctly in classic mode.
  
• Fixed problems with touch input in classic mode.
  
• AI improved a little.
  
• Lots of other tiny tweaks and improvements.