Craft\WebApp and its behaviors do not have a method or closure named "getInfo" Craft\WebApp and its behaviors do not have a method or closure named "getInfo".

appeared today, nothing has been updated or changed.

Any ideas?
Sounds like some of Craft's files are missing.  Try downloading the latest release from buildwithcraft.com and re-uploading the craft/app folder and see if that solves it.

Update:

Since the OP sent a ticket into support, I'll update that re-uploading the craft/app folder solved the problem.