Mugsy is described as 'Linux file integrity monitor. It runs as a daemon and any file modifications made to your system on directories you've specify to monitor are logged locally and optionally sent to your elasticsearch server(s)'. There are four alternatives to Mugsy for Linux, Mac and Windows. The best alternative is Tripwire, which is both free and Open Source. Other great apps like Mugsy are AIDE (Free, Open Source), syschangemon (Free, Open Source) and Samhain (Free, Open Source).
The Samhain host-based intrusion detection system (HIDS) provides file integrity checking and log file monitoring/analysis, as well as rootkit detection, port monitoring, detection of rogue SUID executables, and hidden processes.