Based on the description above, I'll definitely need more details because I'm interpreting two different designs in my head. So first things first, we will need to get clarity on what paradigm you are trying to use. =)
A widget is a legacy terminology that is made available via a plugin, that is written in Java/Spring etc... and only available on Jive On-Premise/Hosted.
A Jive Add-On is the recommended means of extension, that is written using HTML, JS, CSS, REST and available on all instances of Jive (7.0+ & Cloud).
That being said, assuming you are wanting to build an Add-On, a few things come to mind.
If you are looking for something visual, then you are going to want to check out Tiles, Templates & Streams - Developer Resources as Tiles are the "new widgets" if you will.
Some of the words you used above made me think you wanted to listen to when people engaged on content, and then do something else. I would definitely check out REST & Webhooks - Developer Resources ... specifically Webhooks, as they are a means of registering a callback with Jive, such that whenever something happens your external service can be made aware.
To get this all started, I would recommend getting started with either Getting Started > Creating a List Tile with the Jive Node SDK (or if you are a Java person, perhaps giving this a try, Announcing the Jive SDK (Java) Jersey Edition on GitHub Open Source)
Just trying to throw out a big casting net to see if anything catches. Let me know if you need more focused direction, but for now...without more information, this is the best next step I can provide.
If you could share some more specifics, I'll be happy to point you in a more focused direction. =)
Hope this helps.
One thing I would add is that the Ideation module due to being a plugin and not part of the core may or may not have much support in the core API. I haven't looked at it in 6 or 7 but previously it did not have any support in the web services. Somethings might work because it is a registered content type but I would definitely want to look and see it in action before planning too much.
Ideation has support in the V3 APIs for things like Content and Votes. Depending on the requirements it might have some gaps, but hence the reason I was asking for more detail: