One of the most cost-effective, accurate, and cheap methods for radial velocity measurements is the usage of the gas absorption cell (e.g., Iodine cell) method. We present new open-access software for processing spectra obtained with gas cells, the python-based program Viper (Velocity and IP EstimatoR), and recent results obtained with it. It can be used for data obtained with gas cell from multiple instruments (e.g., OES, TCES, CRIRES+) and new can be easily added. When this method was tested on Ondřejov Echelle Spectrograph data, the achieved rms improved 6 times compared to a classic cross-correlation method. Viper is still under development. One of the new features we are currently working on is employing telluric lines that allow us to use Viper for the analysis without a gas cell.