Clockwork Free is very useful, even if it is rudimentary and lacking a lot of the basic functions, tutorials, and interface tools you'll want in an app of this type. It allows you to create multiple timers that chain together to ensure you are performing tasks in the right time frames. The two examples included are studying and exercising, perfect examples of activities where you need to measure multiple small chunks of time in succession.
Upon opening Clockwork Free, you can start using it right away. The two sample activities are already loaded to show you how it works, although there is no walkthrough or tutorial to teach you how to set anything up. Of course, the app is fairly straightforward so that is not a big issue. You can set a new list, and then set various time frames in that list. So if you want to work for 45 minutes and then take a 15-minute break, set two timers: one for 45 minutes and the second for 15 minutes. Not only can you chain these together a near infinite number of times, you can set them to repeat. This is great for exercise where you can set multiple small intervals of five or ten minutes and then repeat them all three or four times.
If you want a timer app that will keep track of multiple small segments of time, then consider Clockwork Free. The app is very bare bones in its design and execution but it works well and provides a useful tool that many people will appreciate.