These fall into a few categories and in each there are viable "off the shelf" solutions that you can include in your site. Using an off-the-shelf solution is often - but not always - the best route to take.
These are electronic versions of those (usually messy) real-life boards where office staff can post any number of announcements. The virtual versions are more organized than their real predecessor. Probably the most
Ondemandacademy.com Blog famous bulletin board is the facebook "wall" but there are lots of others. You may want to have one or more person posting, allow comments, expire notices and send notifications when a new article is posted. Bulletin boards are often used on internal systems (intranets).
Blogs or (Weblogs) are similar to Bulletin Boards but usually postings are made by one person only. Reader comments can be allowed, refused or limited. Wordpress was the first (?) or at least the most popular open source (free) blog website where you could easily create your own blog. Blogs are usually used to post timely articles as you progress through a process. They are often used to post trip activites as the trip progresses or development activites as the creative process progresses. Many people are professional bloggers and can earn substantial income from their blogs. As a rule of thimb if your blog is intended for your membership only or for a private collection of individuals, then a custom blog is a good solution. It is not an onorous task for a programmer to write and can give you quite a bit of flexibility. If you intend to open up your blog to the public at large, use a blog tool like Wordpress.
Forums are similar to blogs except that they are intended for group discussion. There is often (although not always) a forum moderator who will start the discussion topic and members of the forum will comment on the topic and on the comments posted by other members. These are often used in e-learning systems to provide learners with an opportunity to discuss certain concepts. They are also used by many "how-to" reference sites like stackoverflow.com (one that I use a lot). Forums can get to be a lot of work to monitor and many public forums get shut down by the moderator as a result of inappropriate commenting.
Many marketers use one of the available group email offerings currently available on the web (Constant Contact, MailChimp, GroupMail, etc.) These tools are generally quite flexible and, provided you pass the anti-spam tests, you can use these to market you website or product. They are not generally incorporated into your website however which means that you'll have to so some work to coordinate your database of recipients with the tool's database. An alternative is to include a group mail function in the website itself. Gradpass Systems has built several group mail functions that are accessible from the website. Because of the amount of programming required to make the group mail templates as flexible as the commercial options, these internal systems have been used primarily for sending out simple announcements to a specific group of members within the database. The caution with any group e-mail tool is to make sure that you are not violating the generally accepted anti-spam ethics.