Name of the software =
Bogofilter

Project/product Homepage =
http://bogofilter.sourceforge.net/

Why we should include this into the repository, i.e. what does it do that the alternatives do not?
Claws email client gets installed with 3 spam filter plugins, bsfilter, bogofilter and spam assassin but none of these command line tools exist in a solus install and there none in the repos so none of the filters actually work due to the missing command line binaries. Any of these would be ideal but bogofilter appears the more lightweight compared to spamd. bsfilter is ruby code.

Is it open source?
Yes

Source=
https://sourceforge.net/projects/bogofilter/files/
Stable v1.2.4

Extra Info =
Bogofilter is a mail filter that classifies mail as spam or ham (non-spam) by a statistical analysis of the message's header and
content (body). The program is able to learn from the user's classifications and corrections.