What does Free REALLY mean? 
Well, so far I have discovered it could mean 1 of 4 things:

1. It's REALLY free. It could be an organization that wants to get out the 411 or help, or it is the first in a series of Apps and they're giving you a freebie. Buy these freely NO caution here, you can alway delete.

2. in-App Purchases: They give you a taste with the option to buy more. A GOOD example of this is NO Fear Shakespeare. You get 1 free play and then you can in-app purchase other plays. Another is Highlights Hidden Pictures you can get a subscription. I have the same ? with this one. 
Caution Here! Make sure you turn OFF in-App purchases in the setting->General->Restrictions, then you can download these and at least enjoy the full free sample and decide later to buy more.

3. Helper App to a computer based subscription. A good example is QuickInput, they want me to purchase a school liscense of their data management software just to use a (perfectly developed by the way) behavior tracking. I actually hope they have more of these to solve the Java problem. I would really like to use my webbased subscriptions like ALEKS Math, Reading Plus, Brain Pop, etc on the iPod and iPad.

4. Last and probably MOST plentiful: It is only a partial or lite version with features or levels missing. Thing to think about if you are a school account. The lite versions in my eyes have 2 problems: 1- They pollute my Mothership (App Library:) I already have almost 2,000 Apps. As an administrator I DO NOT want to mess with the free "LITE" stuff coming back to haunt me (and they will every time their is an update!) and 2- If it is under $2-3 dollars and the teacher has read through all the description page I want him or her to try the FULL version to review. If purchased with iTunes cards the app can be put on upto 5 devices to review.

Apps that monitor free or discounted apps