The ftp client has some very nice features such as a progress meter, and command line editing thanks to Luke Mewburn. Though to date I've only ported libedit to SunOS 4, so it is not made by default. You still get the progress meter though.
Last time I checked, both client and server are compatible with Tim Hudson's SSLftp. Do not even think of compiling this with a non-ansi compiler. Sorry, while nearly all the code in this tree will compile (and work :-) with the lame compilers bundled with OS's like SunOS and HP-UX, bftp still relies on some ansi features. On Solaris, I found gcc-2.7.2 necessary rather than the 2.5.8 which you may have from an old cygnus CD.
More info about SSLeay can be found in the SSLeay FAQ