Well, Italy neutral is a pretty common scenario here and there are a lot of threads about it.
For this to happen basically everything need to be the same till june 1940 when Benny decide suddenly to become prudent or the King finally grows a pair and say that he will not support a DoW and Italy remain neutral even if France fall, basically accepting whatever 'bribe' the Entente give her.
This mean an open mediterrean, no African front, probably a different management of the French surrender (expecially Dakar and Mers-el-Kebir), very probable no Greece invasion...all this mean that while Germany will save a lot of resources and men, the Entente will save much more and her logistic situation will be much much better.
This is really really bad news for Japan, as British asian holding will not be stripped of the best men and equipment and will be a much harder nut to crack and seen how close things were (expecially Singapore) this mean that the Japanese wave has been pretty much contained ITTL.
The URSS situation much depend if Stalin, without Germany having to fight directly in other plance, believe the various report about an imminent Nazi invasion, if yes the German gain regarding men and resources are nullified by the Red Army being prepared this time...if not, the URSS is up to a much more difficult war and sure she will win but i expect lose more men and gain less territory than OTL due to Germany having more to throw to them.
Italy, well Italy will still commerce with both side and basically being one of the big boys will mean that the Allies will close their eyes if things are not too much open and will try to extract all the concession possible from Greece and Jugoslavia short of invasion, even if due to the pretty volatile situation of the second a civil war is very possible and this will bring an italian invasion.
Once she declare war on Germany and i expect will happen once the writing is on the wall, secure Austria will be the main objective with keeping Jugoslavia out of URSS reach the close second, hell Benny can invade Jugoslavia just to beat the Red Army.
Romania is an important point, with Italy neutral she can intervene when Stalin launch his ultimatum, she had a lot of interest there and OTL she played second fiddle to Germany as there was a war against the British to win first and the URSS was an important supplier for the German war effort at the moment. ITTL is not the case and can at least reduce Stalin demand, keeping Bukovina (and Hertza territory) out of his reach and allowing a more slower Romanian retreat