diff --git a/rust/aura-pm/src/command.rs b/rust/aura-pm/src/command.rs
index d1f82703c..7ba6008db 100644
--- a/rust/aura-pm/src/command.rs
+++ b/rust/aura-pm/src/command.rs
@@ -5,6 +5,7 @@ pub(crate) mod cache;
 pub(crate) mod check;
 pub(crate) mod conf;
 pub(crate) mod deps;
+pub(crate) mod free;
 pub(crate) mod logs;
 pub(crate) mod misc;
 pub(crate) mod open;
diff --git a/rust/aura-pm/src/command/free.rs b/rust/aura-pm/src/command/free.rs
new file mode 100644
index 000000000..18771a6c9
--- /dev/null
+++ b/rust/aura-pm/src/command/free.rs
@@ -0,0 +1,158 @@
+//! License detection.
+
+use applying::Apply;
+use r2d2_alpm::Alpm;
+use std::collections::HashSet;
+use std::ops::Not;
+
+const COPYLEFT: &[&str] = &[
+    "GPL", "AGPL", "LGPL", "MPL", "EUPL", "OSL", "EPL", "CPL", "IPL",
+];
+
+// As found here: https://opensource.org/licenses
+const FOSS_LICENSES: &[&str] = &[
+    "0BSD",
+    "AAL",
+    "AFL",
+    "AGPL",
+    "APSL",
+    "Apache",
+    "Artistic",
+    "BSD",
+    "BSL",
+    "BlueOak",
+    "CAL",
+    "CECILL",
+    "CPAL",
+    "CPL",
+    "ECL",
+    "EFL",
+    "EPL",
+    "EUPL",
+    "GPL",
+    "IPA",
+    "ISC",
+    "IPL",
+    "LGPL",
+    "LPPL",
+    "LiLiQ",
+    "MIT",
+    "MPL",
+    "MirOS",
+    "Motosoto",
+    "MulanPSL",
+    "Multics",
+    "NCSA",
+    "NPOSL",
+    "NTP",
+    "OFL",
+    "OLDAP",
+    "OSET",
+    "OSL",
+    "PHP",
+    "PostgreSQL",
+    "RPSL",
+    "RSCPL",
+    "SPL",
+    "SimPL",
+    "Sleepycat",
+    "UCL",
+    "UPL",
+    "Unlicense",
+    "VSL",
+    "Xnet",
+    "Zlib",
+    "eCos",
+    "QPL",
+    "PSF",
+    "NGPL",
+    "NOKIA",
+    "OGTSL",
+];
+
+pub fn free(alpm: &Alpm) {
+    let lics: HashSet<_> = FOSS_LICENSES.into_iter().map(|s| *s).collect();
+
+    println!("Not using FOSS licenses:");
+
+    for p in alpm.as_ref().localdb().pkgs() {
+        let ls: HashSet<_> = p.licenses().iter().flat_map(parse_licenses).collect();
+
+        if ls.iter().any(|l| lics.contains(l)).not() {
+            println!("{}: {:?}", p.name(), ls);
+        }
+    }
+}
+
+pub fn copyleft(alpm: &Alpm) {
+    let lics: HashSet<_> = COPYLEFT.into_iter().map(|s| *s).collect();
+
+    println!("Not using Copyleft licenses:");
+
+    for p in alpm.as_ref().localdb().pkgs() {
+        let ls: HashSet<_> = p.licenses().iter().flat_map(parse_licenses).collect();
+
+        if ls.iter().any(|l| lics.contains(l)).not() {
+            println!("{}: {:?}", p.name(), ls);
+        }
+    }
+}
+
+// /// All licenses currently associated with installed packages.
+// fn licenses(alpm: &Alpm) -> HashSet<&str> {
+//     alpm.as_ref()
+//         .localdb()
+//         .pkgs()
+//         .iter()
+//         .flat_map(|p| p.licenses())
+//         .collect()
+// }
+
+fn parse_licenses(raw: &str) -> HashSet<&str> {
+    raw.split("AND")
+        .flat_map(|s| s.split("OR"))
+        .map(parse_prefix)
+        .collect()
+}
+
+fn parse_prefix(lic: &str) -> &str {
+    lic.split_once('-')
+        .map(|(l, _)| l)
+        .unwrap_or(lic)
+        .apply(|s| s.trim())
+        .apply(trim_numbers)
+}
+
+fn trim_numbers(lic: &str) -> &str {
+    lic.trim_end_matches(|c: char| c == '.' || c.is_ascii_digit())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn prefix() {
+        assert_eq!("MPL", parse_prefix("MPL-1.1"));
+        assert_eq!("MPL", parse_prefix("MPL"));
+        assert_eq!("GPL", parse_prefix("GPL2.1"));
+    }
+
+    #[test]
+    fn parsing() {
+        let mut set = HashSet::new();
+        set.insert("MPL");
+        set.insert("LGPL");
+        assert_eq!(set, parse_licenses("MPL-1.1 OR LGPL-2.1-only"));
+
+        let mut set = HashSet::new();
+        set.insert("MIT");
+        assert_eq!(set, parse_licenses("MIT"));
+
+        let mut set = HashSet::new();
+        set.insert("MIT");
+        set.insert("BSD");
+        set.insert("SGI");
+        assert_eq!(set, parse_licenses("MIT AND BSD-3-Clause AND SGI-B-2.0"));
+    }
+}
diff --git a/rust/aura-pm/src/flags.rs b/rust/aura-pm/src/flags.rs
index aab7ee766..d18c22b38 100644
--- a/rust/aura-pm/src/flags.rs
+++ b/rust/aura-pm/src/flags.rs
@@ -362,6 +362,8 @@ pub enum SubCmd {
     Stats(Stats),
     /// The people behind Aura.
     Thanks,
+    /// State of Free Software installed on the system.
+    Free(Free),
 }
 
 /// Synchronize official packages.
@@ -1100,6 +1102,14 @@ pub struct Stats {
     pub heavy: bool,
 }
 
+/// State of Free Software installed on the system.
+#[derive(Parser, Debug)]
+pub struct Free {
+    /// Consider only Copyleft licenses.
+    #[clap(long, display_order = 1)]
+    pub copyleft: bool,
+}
+
 /// Synchronize AUR packages.
 #[derive(Parser, Debug)]
 #[clap(short_flag = 'A', long_flag = "aursync")]
diff --git a/rust/aura-pm/src/main.rs b/rust/aura-pm/src/main.rs
index ee13f5d39..fadbd0ddc 100644
--- a/rust/aura-pm/src/main.rs
+++ b/rust/aura-pm/src/main.rs
@@ -63,6 +63,7 @@ use aura_pm::flags::AURA_GLOBALS;
 use aura_pm::ENGLISH;
 use clap::Parser;
 use colored::Colorize;
+use command::free;
 use env::Env;
 use i18n_embed::fluent::FluentLanguageLoader;
 use i18n_embed::LanguageLoader;
@@ -233,6 +234,9 @@ fn work(args: Args, env: Env, fll: &FluentLanguageLoader) -> Result<(), Error> {
         SubCmd::Check(_) => check::check(fll, &env)?,
         // --- Credits --- //
         SubCmd::Thanks => thanks::thanks(fll),
+        // --- Free Software --- //
+        SubCmd::Free(f) if f.copyleft => free::copyleft(&env.alpm()?),
+        SubCmd::Free(_) => free::free(&env.alpm()?),
     }
 
     Ok(())