Acčento is an easy-to-use tool for adding Czech diacritics to copied text. The app lives in the menu bar and is activated using a global hot key.
Activating the global hot key (or using the menu bar option "Acčento!"), your current clipboard is sent to Lingea to add diacritics. The result is analyzed, cleaned up, and written back into your clipboard. It should have nearly the same structure as the copied text. A notification tells you when the diacriticization is done and also how many words are uncertain.
The app also contains preferences allowing you to customize the hot key as well as other quality of life features.
Props to 
for providing the incredible diacritics service.
Visit Releases and download a .zip file of the latest version, open it, move the app into the Applications folder and launch it.
If you'd like to see a feature implemented, feel free to open a pull request or just a proposal as an issue.
This project isn't following any best practices; that said, please try to keep the code clean and simple. Same with commit messages. Thanks!