Ultimate Bulletin Board is a very nice BBS to work with. I haven't checked under the hood (as I'm somewhat new to Perl as well) but from what it says for requirements on their site and it's robustness I'm going to assume it's competently coded.
You can download a demo of here.
The Liscense:
- Modifications of any kind to the UBB Demo Version code are strictly prohibited. You may not alter the program code in any manner, except to change Perl paths, if necessary, or to change absolute paths for required files. You may not add additional code to the UBB Demo.
- You may not distribute, sell, or reuse the program in any manner. In addition, you may not use any code snippets from the UBB Demo for any other purpose without the express written consent of Infopop Corporation. Each download is intended for one customer only.
License and UBB name © 2001 Infopop Corporation. All rights reserved.
A BBS can be a very complex system (I'm speaking as DBA who's done the other side of it) so I can definitely understand needing some reference material. My interprettation of their license is that, as long as you don't copy or modify any code, you can get a feel for how they do it. IANAL though, so it's up to you.
Update:
I haven't been in a project that used UBB in many years, well before the current company (whether they changed their name or bought it) was controlling it. The programmer at that time were okay with it and seemed competent enough, but I'd take
grinder's concerns into serious consideration as potential security issues always bear scutiny.