ToastFish[摸鱼时间背单词]
Fine, Let me use my limited English to tell you about this app 'ToastFish'.

Before introduce, Mac users, you guys can quit, because there is no Mac version :)
unless you want to develop one yourself. (Pls tell me if you really do this)
HOW TO
Of course, the first step is to install
Open this:release
Download this

Install this
Choose a word list

Select the quantity favorite

Click to get start it

After memorizing, there is a little test

Did you get it?
I'm sure the English above is just a breeze for you. Click the link to go to GitHub for the Chinese introduction.
Q&A
Q: The stay time for each notification is too short. How to set the stay time? A: You can set the dwell time in System Settings -> Ease of Use -> Display -> Notification Display Time
Q: Does it crash when using the English pronunciation function? A: Please download the English voice pack in the system settings and restart the software to solve the problem.
Q: Is there any development plan for Win7 or Mac version? A: This is really not the case. Win7 and Mac do not have the notification bar of Windows 10.
Q: What should I do if there are no words I want to memorize? A: You can use the custom function to build a word list yourself. If there are a lot of words, you can contact the author for help adding them.
Q: Encountered other difficulties or want to make suggestions for the software? A: You can raise an issue and provide me with questions or suggestions.
Q: Is there any charge for the software? A: Completely open source and free.