What are all these .gnucash and .log files filling up my directory?
These are backup data files (“.gnucash”; it was “.xac” in versions before 2.4) and log files (“.log”) that GnuCash creates to prevent data loss. Gnucash will remove them after a configurable amount of time (Preferences/General/”Days to retain log files”). In the normal case when your data file is ok and you don’t need old versions of the file, you can remove these files safely.