There's several that play just like Velena, so I won't mention those.

Off the top of my head, there's:

3D Connect Four
John's Connect Four Playground
Conny (doubtful they have this)
Fhourstones (but requires you to compile it yourself)

There was a comprehensive list at the brettspiele site but that appears to be down right now.

fhourstones i never heard of

fstal, how do you compile fhourstones? is it even worth it cos connect4 playground is useless so whats this like? 
thank u.

i just realized it's the same as playground, so no it's not worth it.  To compile it you need a compiler.  It looks like you have 3 options: compile the C++ version, the java version, or the Haskell version (Fhourstones comes with 3 types of files: .c which compiles to .exe, .java which compiles to .jar, and .hs which compiles to i don't know).  I've only tried the C++ version, with a good free compiler "Bloodshed Dev C++" (made by one of my professors), but it couldn't compile it because it said there were programming errors.  I didn't try further than that.  If you wanna try the java version, the java compiler is free at the java site, it's SDK or something.  Haskell i barely know anything about, but there are compilers for it, i think Helium is one.