Fraps was designed to monitor framerates in DirectX and OpenGL games.

The name itself is derived from the term Frames Per Second (FPS) which is what the program displays in the corner of the game's screen. Fraps measures the framerate by monitoring calls to the Flip procedure in DirectDraw. The game calls the Flip function when it is using double buffering and needs to switch between the two surfaces. As an entire screenful of data is transferred from the buffer, the Flip function waits for the vertical retrace of your monitor before writing the new data to the screen.

Fraps will not work with games that do not use buffering (and the Flip function). Games that do not use buffering are ones that do not write large amounts of data to the screen. Typically this will involve games that have static backgrounds and move sprites around (such as War and Real-time Strategy games). What you should be worried about are the rates in games using complex 3D environments, and this is what Fraps works best with.

After version 1.9d, Fraps became a shareware product which hasn't been updated since 2013.