This plugin gives your frontend a calendar, where you can show blocked and free days to your users. A user can click on a free day and register via email. 

How to block and free days again:

1. Install the package from marketplance
2. Login to your site
3. Add the "Registration Calendar" block anywhere to your site
4. Click on "Dashboard"
5. Click on "Registration Calendar" -> "Home"
6. You will see the calendar with only white (free) days
7. Click on a day and let the page refresh. The day is now red (blocked). This is also seen by the frontend user
8. To free a day, click on a red day and let the page refresh. The day is now free again. 

Have fun. E-Mail me for additional support or questions.

Cheers