At Lombiq we believe in open source and empower it how we can: for example we routinely release open source Orchard modules that are freely usable by anyone on their Orchard-driver websites. Recently we created two modules: Watcher and Route Permissions.
Watcher enables users to "watch" content items, i.e. subscribe to notifications if the item changes. The module integrates with the new Orchard 1.7 module Workflows and is thus very generic: you can e.g. send e-mails to subscribed users when a message is posted to their watched forum or if a comment appears under their watched blog post; but not just e-mails, you could set this up to send private messages, sticky notifications, anything that is usable from a workflow. You can get an idea of how Watcher works by reading its documentation.
The Route Permissions module enables you to configure access control for URL patterns defined by regular expressions. This is convenient if you have sections on your website defined by a directory structure (e.g. blog/private vs blog/public) as you can use such URL patterns to quickly restrict access to a bigger part of the site.
If you have any questions about our modules or need help about something don't hesitate to drop us a mail.
You can view all of our open source modules under our company profile on Codeplex.