Books cost money and require the user to read them for the idea to spread.

They usually do not require the user to make a specific payment to the author.

It does not require the user to program in any language other than Java.

It is empty and therefore requires the user to input data.

All of this is possible without requiring users to install software on their own computers.

It does not require the user to be able to construct the character from scratch as one would do in writing Chinese.

Making a prepaid or calling card call requires the user to make two calls.

The software requires the user to play music from these sites, in the web browser.

Not long ago, each of these functions required the user to buy a freestanding software program.

This requires the user to bend over at the waist with every swing.