Can the Xero accounting package be integrated with CiviCRM?
There has been some integration work undertaken by Fuzion and is available in this extension. General functionality:


create contacts in Xero based on them being created (or having had a contribution or recurring contribution) created in CiviCRM. You can configure which of those 3 will cause them to be created in Xero
update contacts in Xero based on the contact or contact details having been updated in CiviCRM
adds a link to the contact summary to the Xero record
adds a link from the contact summary to the contact's transaction history in Xero
creates invoices in Xero based on contributions in CiviCRM (and adds a link in CiviCRM)
where a pending contribution has a payment matched in Xero the CiviCRM contribution is updated (which participant records, memberships etc also being updated &amp; emails sent as configured)
where a contribution is voided or cancelled in Xero it can also be cancelled in CiviCRM


The extension cannot be downloaded through the UI (intentionally) as it defintely requires someone technically savy to be involved in setting it up &amp; maintaining it. You can see much of what is possible at this blog post