Captivate interface is similar to PowerPoint. In Captivate you have the deck of slides on the left column and the stage in the middle area. Each slide has an individual timeline that works independently. You add all the elements you need into the same "stage" area. If you need more time per slide, you have to stretch the slide to accommodate the information.
Camtasia reassembles the workflow of a movie editor such as iMovie or Vegas. This program assembles projects as a continuous video. You add element such as text, graphics, and audio to the same timeline in different tracks as necessary. Each element you add occupies an specific space in the timeline. You may add or stretch elements in the timeline as needed.