Free should mean completely without cost at point of download and that all features of the software are available to use without upgrading or purchasing subscriptions. Free software can have adverts within it, but nothing that pops up or forces you to read or click before letting you use it.
It could be argued that no software is completely free in our modern world, due to the fact that even entering your name, email and other basic details to log in could be valuable to the developer; data about users is very valuable these days.
The freemium business model is not a completely new idea but it is certainly much more widely used nowadays than it has been previously. Freemium means that software is given away for free at point of download and should offer enough features to make it useful and usable. Certain “premium” features will be behind a paywall, requiring you to upgrade or subscribe before you can use them. A good example of this is Skype.
Skype now comes preinstalled with Windows 10 and offers you completely free PC to PC Internet calls, as well as instant messaging and other features. If you want voicemail, conference calls or connection to landlines, you will have to pay a fee.
Ad-supported software, as the name suggests, is free software that is supported (financed by) adverts. These could be in the form of pop-up and pop-under adverts, small ad panels within the software interface or splash adverts that you are forced to watch for a few seconds before the software interface is shown.
Often, ad-supported software will offer the ability to turn off the adverts by paying a small fee. Some freemium software will also remove adverts for paying users.
Trialware is free software with a built-in time limit. You can try out the fully featured program until the trial period is up, normally 14-28 days but sometimes much shorter, and then most trialware reverts to a reduced or non-functional mode. If you decide to pay the fee, you will receive a registration code to unlock the program. Trialware has become the norm for online Software as a Service (SaaS).