BPALogin (http://bpalogin.sourceforge.net/) it works on many different platforms (Windows/UNIX/BeOS) with a very small footprint size. Source for all platforms is available
Bids2login (unknown) - a PERL script written by an ex-BPA contractor. Unsupported.
BPC_NO (unknown) - a JAVA based client written by David Seikel
I haven't used the other 2, so I will just detail how to get BPALogin working. There are numerous packagings of BPALogin, but there are 4 that relate to Linux
bpalogin-1.5-3.i386.rpm - RedHat 6.x & Mandrake 7 RPM file, will only work on x86 systems
bpalogin-1.5-3.src.rpm - RedHat 6.x & Mandrake 7 SRPM file. If you have a non-x86 (like a Sparc) system, you can do a rpm -rebuild bpalogin-1.5-2.src.rpm and create a new package. This method also works if you have RedHat 5.x (which has an older version of glibc)
bpalogin-1.5-unix.src.tar.gz - a standard UNIX Tarball. This should work with all Linux's, Solaris, SunOS, and most Unixes.
bpalogin-1.5-precomp-linux.tar.gz - a precompiled x86 version for Linux systems with kernels >= 2.2. This should work on all x86-Linux's
