Very large file located within ~/Library/Group Containers/group.com.lminhtm.tempmonitor/db.realm
Group Containers are basically Containers, which are sandboxes for applications to store date (user data, caches, logs, etc), except the Group part means that it's at a developer level. This could be used to, for instance, keep a user logged into the same account across multiple apps made by the same developer. That said, it could be used for anything, which is what this appears to be. 

You could check with the developer, in this case: https://github.com/lminhtm. Otherwise, I'd make a backup and delete (or just move it to a different location), then test any apps you have from this developer (maybe this one?).