Not so sure but, the only "maintained" Perl based forums are YaBB & e-Blah.

On what grounds are you discounting mwForum?

mwForum doesn't have an external API feature either, but unlike most of the inexplicably popular UBB clones it does have an internal plugin API, meaning you can extend it without modifying the original code.

In reply to Re^2: Perl based forum code that has good API by Porculus
in thread Perl based forum code that has good API by datamonk

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