Added the original reference. Removed the following discussion to the nForum:

David Roberts: A couple of years ago I thought of importing topological groupoids to this concept for the following reason: The tangent microbundle $M\times M$, when $M$ is a manifold, is the groupoid integrating the tangent bundle $TM$ of $M$. If we have a general Lie groupoid, we can form the Lie algebroid, which is a very interesting object. If we have a topological groupoid, it seems to me that there should be a microbundle-like object that acts like the algebroid of that groupoid. This should reduce to the tangent microbundle in the case of the codiscrete groupoid = pair groupoid. Perhaps not all topological groupoids would have an associated algebroid, but those wih source and target maps that are topological submersions probably will.

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Anonymous

]]>Tim Porter added references to microbundle and I edited the formatting of the entry a bit

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