Based on the open source project Caffeine.
Caffeine-Simplified is a small utility program that prevents your computer from going to sleep without having to change Windows' settings. It runs as a tray icon and can be enabled or disabled by clicking on it.
Or use the menu by right-clicking it.
Caffeine-Simplified since v1.0.4 should work on Windows 7 or later, both 32-bit and 64-bit versions.