App X could be Microsoft Money, QuickBooks, Sage, KMyMoney, Gnucash, Grisbi and others
Source: mail list: ledger.smb.user (Chris Travers and others)
With unknown programs you need to to find out:
1) How much data can you get out?
2) What database system does it use on the back-end?
3) If you cant export data, are there other means (i.e. custom ODBC
drivers, cvs export) that can access the info?
If you can get that information, you are about 50% of the way there.
A few pointers about such migrations :
1) Import into holding tables that match the existing schema of your
old application first. This gives you a backup in case you need to
re-import the data in order to get it right.
The doc is work in progress..., (all the help we get makes it better..)
but you my start with this:
This tread has some info (Jan. 2012)
3) If you get stuck in specific areas, ask on the mailing list or irc, we may be able to be of more help