Busy and Marg each export differently, and neither writes a single file that carries everything the way a Zoho or Odoo backup does — expect to bring masters and reports across as separate files.
Busy
Administration → Data Export Import → Export Data → Masters (Accounts, Items) → Excel. On Standard and Enterprise, the same screen can export XML too, when your version supports it. Basic exports Excel by report only — there is no XML option on that edition.
Marg
If Marg's Tally bridge is set up: Bridger → Tally Export writes a Tally-format XML of ledgers, items and vouchers — drop it on the same Pick screen and it is read like Tally's own Day Book. Without the bridge: Bridger → Export → Masters (ledgers, items) as CSV, then Reports → each report → Excel, and map the columns on the next screen.
What comes across today
Parties, items, your chart of accounts with opening balances, invoices, bills, payments and journals — from whichever export you bring.
What is deliberately not copied
Filed GST returns, IRNs and e-way bills stay with the portal that issued them. Bank-statement matches and attached files are not copied either. Busy's own print formats and user rights stay in Busy; Marg's scheme masters and rate lists stay in Marg.
After you drop the file
Same five screens as every other source — matching columns, a dry run with a verdict on every record, then Import and Reconcile. The mechanics (and how undo and re-imports work) are in Import your data from Zoho, Odoo, Vyapar or a spreadsheet. Back to the full list of sources.