Right now Steam, Epic, GOG, PS4 and Xbox have an achievement system. Will itch.io add an achievement system? Gamerzilla is not tied to any store. With enough support game developers will consider Gamerzilla achievements a needed feature. Additionally this is the only system that all open source games can use.
Initialization code is simply calling GamerzillaStart and GamerzillaConnect. GamerzillaConnect is only needed to upload results. Achievements can be displayed locally without connecting.
GamerzillaStart(true, "save/");
GamerzillaConnect("http://hubzilla.instance/", "username", "password");
There will need to be a thread periodically calling GamerzillaServerProcess to get information from games and relay it to the Gamerzilla server (if connected). To avoid manually configuring the Gamerzilla short name with each game, it is good to install a callback for activity. The callback provides the Gamerzilla short name and the game name so that you can automatically match up the information.
To get achievement information, you call the GamerzillaGetGame function to get the game ID. With the game ID, you can get the number of achievements, which have been achieved, and details of the achievements. GameHub support for Gamerzilla has been submitted to the project if you need an example implementation. Feel free to email dulsi@identicalsoftware.com if you have any problems.