In theory you should be able to use ANY npm.js package. 

Like this calendar https://community.servicenow.com/community?id=community_article&sys_id=458c426d1b9c9010d01143f6fe4bc...

 

I am currently trying a different calendar that my colleague have used in Service Portal so to have a unified look I want to use the same but have not gotten it to work yet. I am almost certain it is just me not doing it right so still have some work to do on that.