Frolic is a moderate Linux box, which needs quite a lot of enumeration getting the user access, but has a nice not-to-hard challenging way to root using Buffer Overflow.
Bastard is a Windows machine with interesting Initial foothold. There is some PHP knowledge needed, although the changes need to be done for the exploit code are pretty minimal. There are more than one way to get into machine!
Devel is a relatively easy hackthebox Windows machine, which can be done almost all the way with metasploit.