This app was mentioned in 11 comments, with an average of 2.55 upvotes
There have been a bunch of websites/apps that you could access for free, but some of them are offline, where you could practice numbers in korean.
The best app left, i found is called Rieul "Korean" and is only available on android.
You could install bluestacks on windows and run that app, if you dont have android like me.
https://play.google.com/store/apps/details?id=com.rieul.rieulkorean&hl=en_US&gl=US
It has various exercises to practice numbers, with multiple, choices, audio, etc.
This app called Rieul Korean is great. It has a dictionary among other things and combines the Naver and Daum online dictionaries.
The creator /u/RieulKorean is also on reddit.
If you've got an Android phone or tablet, you could try my app Rieul Korean, which features, among other things, a conjugation quiz.
This is the best drilling app i found for numbers.
https://play.google.com/store/apps/details?id=com.rieul.rieulkorean&hl=en_US&gl=US
You can test for dates, time, money, age, etc. with audio, typing or multiple choice, etc.
If you dont have android, you can install bluestacks for instance on your computer.
Its also nice for conjugation and pronunciation, etc.
drilling drilling drilling
there are various apps, as people posting here.
some apps also have not only reading but also listening drilling.
this is the android one i run on bluestacks on my computer
https://play.google.com/store/apps/details?id=com.rieul.rieulkorean&hl=en\_US&gl=US
You could try the numbers quiz section of my Android app Rieul Korean to test yourself on native/Sino-Korean numbers, dates, times, money, age and a few counters.
If you have an Android device, try Rieul Korean for pronunciation reference and self-testing.
Rieul Korean has Pronunciation category with the rules and a Test tab with random words.
https://play.google.com/store/apps/details?id=com.rieul.rieulkorean
I haven't used it that much so I cannot really say how good it is.
Nice. Here's the link: Rieul Korean