OSSEC is a free cyber security tool that is used to detect intrusions in the network. This tool is capable of providing the analytics of the security of the system in real time. Users can monitor all the possible points that can give unauthorized access to users. These includes files, processes, logs, etc. OSSEC can be used on multiple platforms like Windows, Mac, ESX, etc. which is the cause for its wide use.
Download Link- https://github.com/ossec/ossec-hids