I would not say it is completely free as you need to have the system for installing the software and internet to run it.
CGMinerCGMiner is the best Bitcoin mining software, which has been around for a while because of a plethora of features and community acceptance. CGMiner is the cross-platform Bitcoin mining software that supports Windows, Mac, Linux, OS X, and many other platforms, thus proving it to be the overall winner. CGMiner is a command-line application, that has complete monitoring, remote interface capabilities, and fan speed control.
The best part about CGMiner is that it can scale to hash rate of any size as it comes with a scalable network scheduler, plus it is compatible with both ASIC (application-specific integrated circuit) - like Hexfury and BlackArrow to Cointerra and Minion and FPGA (Field Programmable Gate Array) software. It supports multiple pools with intelligent failover mechanisms and prevents stale work submission on new blocks.
MultiMinerFor the newcomers, MultiMiner is one of the best Bitcoin Mining software as it is comparatively very easy to use, even for users who are new to this. MultiMiner (famous coin miner) is a desktop-based software, which is embedded with a variety of features like automatic detection of network devices, even has the ability to monitor and control other MultiMiner rigs, remotely. It is available for Windows, Mac, Linux, and other platforms as well.
MultiMiner lets you switch mining devices like ASICs, FPGAs between different cryptocurrencies (e.g. Litecoin, Bitcoin) without any effort. It uses the mining engine to detect the software and lets you choose which of the cryptocurrencies to mine.
MultiMiner is the best software for first time users and it is compatible with many mining devices like Block Erupter or Bitforce, HashBuster Micro.
source: https://coinswitch.co/news/top-10-best-bitcoin-mining-softwares-2020-latest-bitcoin-mining-software-review