Since this is an ad-hoc signed app, macOS Gatekeeper might block it on the first run.
Please follow these steps to open it normally: 1. If a dialog says "Apple can't check app for malicious software", click OK. 2. Open System Settings > Privacy & Security. 3. Under the "Security" section, locate Nikki Albums and click Open. 4. Click Open Anyway, enter your login password, and click OK.