A very interesting article about upgrades planned for the M4 Sherman tank before the war ended and cancelled them.
Co-ax M2 and M1919: A more conventional way was the installation of an M2 .50 caliber Machine gun, alongside the .30 caliber M1919 machine gun, mounted coaxially with the main gun. This would have worked out better if one of the advanced guns mounts using a concentric recoil system had made it into production. I’ll cover these mounts later in this post.
Fragmentation grenade mounts, mines, and pipe bombs: The Army decided to try mounting these on tanks and test how they would work to combat close in enemy infantry as a kind of last resort weapon. This did not work very well and only the grenades were found to have an effective fragmentation effect. They all risked damage to the tank so they were dropped. Shielding to protect the tank made them even less effective. None of these worked as well as having close infantry support, and the idea was dropped.
There is a lot more at the link to the article. You can read it all there.