There are any number of open source and/or freeware applications available to manage your testing activities. Which to choose depends very much on your test management requirements.
What do you need it to do?
- document your test cases
- track test case execution
- record and track defects
- interact with requirements tracking tools
- support automated test execution
- reporting and analysis capabilities
- to name a few
A common starting point, and certainly a low-cost one, is to set up some spreadsheets to manage the information used in your test process.