Engels assisted in writing the communist manifesto, but he was not given aclaim on such a wide scale like marx, why?
Did Engels hold a distinct philosophy from Marx? If so, why isn't that philosophy very popular?
As a follow up, to what degree was Engels involved in projects with Marx? Is it fair to say the Manifesto was just as much his, and was his editing of Capital substantial?
There are at least two reasons (though I expect a more in-depth answer would list many more). The first is that the academic foundations of communism owe more to Marx than to Engels. Engels states this himself in the preface to the 1883 German Edition of the Communist Manifesto:
The basic thought running through the Manifesto — that economic production, and the structure of society of every historical epoch necessarily arising therefrom, constitute the foundation for the political and intellectual history of that epoch; that consequently (ever since the dissolution of the primaeval communal ownership of land) all history has been a history of class struggles, of struggles between exploited and exploiting, between dominated and dominating classes at various stages of social evolution; that this struggle, however, has now reached a stage where the exploited and oppressed class (the proletariat) can no longer emancipate itself from the class which exploits and oppresses it (the bourgeoisie), without at the same time forever freeing the whole of society from exploitation, oppression, class struggles — this basic thought belongs solely and exclusively to Marx.
And again in Socialism: Utopian and Scientific:
These two great discoveries, the materialistic conception of history and the revelation of the secret of capitalistic production through surplus-value, we owe to Marx. With these discoveries, Socialism became a science.
And in his speech at Marx's grave:
On the 14th of March, at a quarter to three in the afternoon, the greatest living thinker ceased to think.
The second reason is Marx's visibility as a revolutionary. His public involvement with the First International helped build his international reputation while Engels remained more of a background figure.