REAPER (Rapid Environment for Audio Production, Engineering, and Recording)
For personal use, or if your yearly gross revenue from REAPER use is under $20,000.
If you decide to purchase a Reaper license, you can do so from the Cockos website. The license fee is relatively low, with a personal license costing $60 (or $225 for a business license). Once you've purchased a license, you'll receive access to official support, updates, and bug fixes.
This "honor system" is a deliberate choice by lead developer Justin Frankel. It treats the user as a peer rather than a potential thief. However, this trust is often misinterpreted. Users looking for a "free licenser" are essentially searching for a way to remove a five-second reminder from a program that already gives them everything for free during its evaluation phase. The Dangers of Unauthorized "Licensers"