This problem occurred after an update from Windows 8 to Windows 10.
Several different apps (shown are Carbonite Backup, and Atlassian SourceTree) have replaced a standard sans-serif font (I think Tahoma?) with this stylized font.
I have seen this before, on a different machine a long time ago, even back to Windows 7 and previous versions, and so I thought perhaps a standard font file was overwritten, or corrupted?
Any ideas? I do have many commercial and freeware fonts installed on my system (1,577 total).
UPDATE: I have checked the default system fonts (Arial, Tahoma, Verdana) in Windows Fonts control panel, and they are not corrupt, displaying correctly.
UPDATE: The font being displayed appears to be Jungle LIFE.