Looking up/ mapping a value across tabs

[fatowl]

Good morning all,
I have a requirement to do a lookup, which i believe might need a 3d function.
I have a spreadsheet that has multiple tabs that depict different areas in various applications. And one tab that has a list of requirements. Within the various application tabs, against each line item I have the requirement it is mapped to. What I am looking to do is in the requirement tab, have one column that has list of all the applications that are mapped to this requirement. An example is as below - the last table depicts what the resultant output should look like (in the bolded column):
Application A tab:
[TABLE="width: 500"]
<tbody>[TR]
[TD]Screen ID[/TD]
[TD]Req ID[/TD]
[TD]Screen Name[/TD]
[TD]Comment[/TD]
[/TR]
[TR]
[TD]123[/TD]
[TD]1[/TD]
[TD]Test 1[/TD]
[TD][/TD]
[/TR]
[TR]
[TD]456[/TD]
[TD]1[/TD]
[TD]Test 2[/TD]
[TD][/TD]
[/TR]
</tbody>[/TABLE]

Application B tab:
[TABLE="width: 500"]
<tbody>[TR]
[TD]Screen ID[/TD]
[TD]Req ID[/TD]
[TD]Screen Name[/TD]
[TD]Comment[/TD]
[/TR]
[TR]
[TD]789[/TD]
[TD]1[/TD]
[TD]Test 3[/TD]
[TD][/TD]
[/TR]
[TR]
[TD]ABC[/TD]
[TD]2[/TD]
[TD]Test 4[/TD]
[TD][/TD]
[/TR]
</tbody>[/TABLE]

Application C tab:
[TABLE="width: 500"]
<tbody>[TR]
[TD]Screen ID[/TD]
[TD]Req ID[/TD]
[TD]Screen Name[/TD]
[TD]Comment[/TD]
[/TR]
[TR]
[TD]DEF[/TD]
[TD]2[/TD]
[TD]Test 5[/TD]
[TD][/TD]
[/TR]
[TR]
[TD]HIJ[/TD]
[TD]1[/TD]
[TD]Test 6[/TD]
[TD][/TD]
[/TR]
</tbody>[/TABLE]

Requirements Tab: (desired result)
[TABLE="width: 500"]
<tbody>[TR]
[TD]Req ID[/TD]
[TD]Requirement Name[/TD]
[TD]Mapped Application Screen IDs[/TD]
[TD]Comment[/TD]
[/TR]
[TR]
[TD]1[/TD]
[TD]Req1[/TD]
[TD]123,456,789,HIJ[/TD]
[TD][/TD]
[/TR]
[TR]
[TD]2[/TD]
[TD]Req2[/TD]
[TD]ABC,DEF[/TD]
[TD][/TD]
[/TR]
</tbody>[/TABLE]