OS=Kubuntu 14.04
Subject kind of describes it. You know when the light bulb in your head goes off and 5 mins later you are scratching your head? Ever totally forget to do something important because you were making sure ALL of your FLAC's names were in a standardized form.

I have an entire monitor I can dedicate to this app (if needed) mounted in portrait position.

I need to input tasks/ideas as quick as possible b4 I forget and then cross off as completed.

I looked through this forum an didn't see much mentioned but google search yielded some results like:
Task Coach
Toodledo
Todo.txt
Probably many more, I just don't know which.

I would prefer to have everything reside on my system (not hosted online unless it is on my web server) and sharing on a LAN would be nice.

Anyone have any ideas of what software might be available for this?

Not an application, but a free, or you can choose to pay, online tool.

Consider using Trello.

The benefit is that you can access it on multiple systems including a smart phone.

I put everything in text files, which I share among my zillion systems via Dropbox.

Paper-based notebooks, by the way, are great as well, especially when it comes to diagrams. The sharing aspect is a bit underdeveloped though.

zim-wiki

For my own uses it does not get any better than TaskWarrior.

*** UPDATE - while linking I noted a new release today, 10/21/15 - v2.5.0. Now built and working on my systems, all good!

Use org-mode in Emacs