I have no idea what that is but if you manage to culture it, you have just started a new business
I assume it is in a freshwater tank?
Is the blue stuff hard or soft when you touch it?
Hard would suggest a calcareous algae but they are rare in freshwater and I have never seen one that colour. Or a mineral deposit but there aren't any blue minerals that look like that.
Soft could be something else like a sea squirt but they are normally saltwater.
How long has it been there for?
What have you added to the tank during the 2 weeks before it appeared?
What is it growing on?
How hard is your water? Go to a petshop and have them check the GH, KG and calcium if you can. Petshops that sell corals and marine fish should be able to test the calcium level in your tank and tap water.
Clean your glass down and take some more pictures of it. If it moves about then video it. This is quite interesting
The following link is of coralline algae in freshwater. There are several threads on forums about coralline algae in freshwater and they all appear to be in hard water. If your water is very hard, you could have a rare and very cool, coralline algae that everyone is going to want.
https://www.advancedaquarist.com/blog/discovery-of-first-freshwater-coralline-algae