Binfilter was a set of legacy filters, abandoned by LibreOffice because it was too difficult to maintain.
Some projects provide a version of binfilter, e.g. here's the package from Debian Wheezy. Here's the description of the package:
This package contains the "binfilters", legacy filters for
- the old StarOffice 5.2 formats - StarWriter 1.0/2.0 - StarWriter/DOS - *Writer* filters for + Excel + Lotus
The DLP project libraries have replaced much of the functionality provided by binfilter.
Getting the source
The source code is available in gerrit.
Building the code
There's GSoC Project Proposal to implement a modern alternative to binfilter.