It would be nice if the software had a book close feature.
Here is how I think it should work:
When invoked it would take the balance of every expense and income account at the book end date (usually 31/12/YYYY) and include a transaction to make this balance zero. The other end of the transaction would be an equity account to be defined by the user. It would be preferable to use splits to do this to reduce pollution in the equity account used. Gnucash has this feature and I believe it would be useful for jGnash as well.