If you’re researching your family history in Ireland, you might be interested in the Irish Archives Resource. It’s a new, searchable database containing archival descriptions of manuscripts at 34 repositories and Archive Services throughout Ireland, including the National Archives of Ireland and Public Record office of Northern Ireland.
The site started as a pilot project with four repositories in 2008. It doesn’t contain historical records, but it does help you find repositories holding those records.
According to the Family History/Genealogy page, the Irish Archives Resource portal is “suitable for family researchers who have already discovered some facts about their family history”