Vyapar, myBillBook and Book Keeper each write a Tally-format XML export as well as their own Excel reports. The Tally-format export is the faster path. It is read directly, the same way a Tally Day Book is, and carries masters and vouchers in one file.
Vyapar
Reports → Party Report → Excel; Reports → Item Report → Excel for the two masters. Or Menu → Utilities → Export to Tally for an XML of your masters and vouchers together. Drop it on the same Pick screen and it is read like Tally's own Day Book export.
myBillBook
Reports → Party Statement and Item Report → Download Excel for the masters. In myBillBook, Settings → Export to Tally writes an XML of parties, items, sales and purchases, but payments and expenses are NOT in that export; bring those across from the report Excel instead, as a second file.
Book Keeper
Reports → each report → Export to Excel, one report at a time. Or Export → Tally XML for masters and vouchers together. Drop it on the same screen; it is read like Tally's own export.
What comes across today
Parties, items, your chart of accounts with opening balances, invoices, bills, payments and journals, whichever file you bring, Excel or the Tally-format export.
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. Vyapar's own bill layouts and loyalty points stay in Vyapar; myBillBook's reminder history and its own bill formats stay in myBillBook.
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.