I've made a 1.0 release. See the first post for details. The major improvements are a new friendly greeter dialog, built-in beginner tutorials, undo/redo when editing, and post-game IGS chat directly in the board window.

The bump to 1.0 indicates that this now really is reasonably feature-complete, and it seems stable in everyday use. However, I still have some ideas for the future: half-finished code exists for direct online play without a server, and a new IGS observer window that can switch between multiple observed games, with clickable previews. These might make it into future versions. Other ideas include a built-in beginner bot, and a tsumego module.

bernds, thank you very much! KataGo works 13x19, 4x19, etc.

I choose a game against 13x19 KataGo, then I play. How to start a new game without restarting the program?

For a moment I didn't know what you mean, but I'm guessing the problem is that you used the "Play against the machine" button in the greeter dialog and that got closed? In previous versions q5go didn't have the greeter and started by showing the IGS client window, and that one sticks around when you open board windows. So you can work around the issue for now by choosing "Play online" and then use the client window as before.

I'll make a note to add something like a "Restart game" option for engine games.

Can I configure two programs for playing with each other? for example KataGo - KataGo 19x13?

Yes, it's a menu option in the client window (which used to be the main window). I still need to find a good way to expose these lesser used options in the greeter dialog.

big request, you can give an example of how to do it!
edit: I found! it was where I did not expect! I am happy as a child! thank you very much! I am so tormented with Sabaki
if so: play online or a match between two programs?

I don't understand the last question - was that part of the original problem where you couldn't find the option? The "Computer vs computer" menu item runs a game, or a multi-game match, locally between two engines. Nothing on-line is involved.

To see the client window, you must click the "play online". I didn’t find another way.
I suggest adding a "Computer vs computer" to the “play online” window to make it clear how to launch this. or add the window "Computer vs computer"