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:

Screen ID	Req ID	Screen Name	Comment
123	1	Test 1
456	1	Test 2

<tbody>
</tbody>

Application B tab:

Screen ID	Req ID	Screen Name	Comment
789	1	Test 3
ABC	2	Test 4

<tbody>
</tbody>

Application C tab:

Screen ID	Req ID	Screen Name	Comment
DEF	2	Test 5
HIJ	1	Test 6

<tbody>
</tbody>

Requirements Tab: (desired result)

Req ID	Requirement Name	Mapped Application Screen IDs	Comment
1	Req1	123,456,789,HIJ
2	Req2	ABC,DEF

<tbody>
</tbody>