Data organiser's unusually desperate about call for peace (11)
I believe the answer is:
spreadsheet
'data organiser's' is the definition.
(a spreadsheet is used to organise data)
'unusually desperate about call for peace' is the wordplay.
'unusually' indicates anagramming the letters.
'about' indicates putting letters inside.
'call for peace' becomes 'sh' ('sh!' is a request for silence).
'desperate' with letters rearranged gives 'spreadeet'.
'spreadeet' placed around 'sh' is 'SPREADSHEET'.
(Other definitions for spreadsheet that I've seen before include "Computer program useful for accounting" , "Table-creating software" , "Computer program allowing easy entry, tabulation and manipulation of figures" , "Data manipulation program" , "Figure manipulating program" .)