Ring My Bell

There is a new feature now to post the Alert to a Chatter Group, which is great for spreading the news to non-salesforce users in the organisation. 

On install ensure you select ‘Grant access to all users’

https://appexchange.salesforce.com/servlet/servlet.FileDownload?file=00P3000000HTDo3EAH

• Ability to set up different chatter text for different amounts or Opportunity Types

• Ability to post to different chatter groups for different Opportunity Types

• Ability to modify the text of the alert and chatter post. 

Group Alerts for Chatter does custom alerts for Chatter Groups, so can do the Group alerts part of this app, but not the bell ringing. So, it's much of a muchness - if you just want Opportunities, use Ring My Bell, but if you want other alerts in the group then use Group Alerts.