To remove the software from your computer, delete the following files:
The executable file Abyss Web Server.
The configuration file abyss.conf.
The persistency file persist.data.
The Mac OS X/macOS application preferences file com.aprelium.AbyssWebServer.plist located in your Home folder inside the sub-folder Library/Preferences.
The Mac OS X/macOS launch daemon description files com.aprelium.AbyssWebServer.plist and com.aprelium.AbyssWebServer.HelperTool.plist both located in the system folder /Library/LaunchDaemons.
The helper tool com.aprelium.AbyssWebServer.HelperTool located in the system folder /Library/PrivilegedHelperTools/.