Supermicro has a number of servers with a similar form factor. The closest to a classic HP Microserver is the SuperServer 5028A-TN4, although that one uses the

Supermicro has a number of servers with a similar form factor. The closest to a classic HP Microserver is the SuperServer 5028A-TN4, although that one uses the Atom chips that have been recalled. There's also the much more powerful SuperServer 5028D-TN4T. They also have a bunch of older models whose names escape me, but can be found by searching for "supermicro mini tower".