AIDE (Advanced Intrusion Detection Environment) is a file and directory integrity checker. It creates a database from the regular expression rules that it finds from the config file. Once this database is initialized it can be used to verify the integrity of the files. Several message digest algorithms are used. All of the usual file attributes can also be checked for inconsistencies.
rgxg (ReGular eXpression Generator) is a C library and a command-line tool that generate (extended) regular expressions. It can be useful for generating expressions that match, for example, a specific number range (e.g. 0 to 31 or 00 to FF) or all addresses in a CIDR block (e.g. 192.168.0.0/24 or 2001:db8:aaaa::/64).