Here are some softwares created by Guokai(Jackie) Han
Advanced Form Notifications
Advanced Form Notifications is a Google form add-on, it can help you send email notifications to users and you, and can check new responses or close the form.
Outdated Doc Detector
Outdated Doc Detector is a Chrome extension. It can check whether the translation page is behind the corresponding English version.
A redesigned, productive and pragmatic newtab alternative.
Gmail Add-on for YouTube
GMAYT is a Gmail add-on for YouTube. When you open an YouTube email notification you subscribed, it can show you more information about the video.
Contact Manager for Gmail
Contact Manager is a Gmail add-on that integrate Google Contacts with Gmail. It can list, edit contacts in the email or create new contacts.
Gmail Debugger is a Gmail add-on. It can show gmail's raw and meta data. This add-on is mainly for developers.