diff --git a/Cargo.lock b/Cargo.lock
index 5b0a48c..b7b5755 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -494,6 +494,19 @@ dependencies = [
  "libc 0.2.36 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "semver"
+version = "0.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "semver-parser 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "semver-parser"
+version = "0.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "serde"
 version = "1.0.27"
@@ -759,6 +772,7 @@ dependencies = [
  "mime_guess 1.8.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "nfd 0.0.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "phf 0.7.21 (registry+https://github.com/rust-lang/crates.io-index)",
+ "semver 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde 1.0.27 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 1.0.27 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_json 1.0.9 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -830,6 +844,8 @@ dependencies = [
 "checksum scoped-tls 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "f417c22df063e9450888a7561788e9bd46d3bb3c1466435b4eccb903807f147d"
 "checksum security-framework 0.1.16 (registry+https://github.com/rust-lang/crates.io-index)" = "dfa44ee9c54ce5eecc9de7d5acbad112ee58755239381f687e564004ba4a2332"
 "checksum security-framework-sys 0.1.16 (registry+https://github.com/rust-lang/crates.io-index)" = "5421621e836278a0b139268f36eee0dc7e389b784dc3f79d8f11aabadf41bead"
+"checksum semver 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)" = "1d7eb9ef2c18661902cc47e535f9bc51b78acd254da71d375c2f6720d9a40403"
+"checksum semver-parser 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)" = "388a1df253eca08550bef6c72392cfe7c30914bf41df5269b68cbd6ff8f570a3"
 "checksum serde 1.0.27 (registry+https://github.com/rust-lang/crates.io-index)" = "db99f3919e20faa51bb2996057f5031d8685019b5a06139b1ce761da671b8526"
 "checksum serde_derive 1.0.27 (registry+https://github.com/rust-lang/crates.io-index)" = "f4ba7591cfe93755e89eeecdbcc668885624829b020050e6aec99c2a03bd3fd0"
 "checksum serde_derive_internals 0.19.0 (registry+https://github.com/rust-lang/crates.io-index)" = "6e03f1c9530c3fb0a0a5c9b826bdd9246a5921ae995d75f512ac917fc4dd55b5"
diff --git a/Cargo.toml b/Cargo.toml
index 212753e..6a2ee50 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -23,5 +23,7 @@ toml = "0.4"
 
 nfd = "0.0.4"
 
+semver = "0.9.0"
+
 [build-dependencies]
 includedir_codegen = "0.2.0"
diff --git a/src/config.rs b/src/config.rs
index 3d3be6b..740429b 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -7,12 +7,20 @@ use toml::de::Error as TomlError;
 
 use serde_json::{self, Error as SerdeError};
 
+/// Description of the source of a package.
+#[derive(Deserialize, Serialize, Clone)]
+pub struct PackageSource {
+    pub name : String,
+    pub config : toml::Value
+}
+
 /// Describes a overview of a individual package.
 #[derive(Deserialize, Serialize, Clone)]
 pub struct PackageDescription {
     pub name: String,
     pub description: String,
     pub default: Option<bool>,
+    pub source: PackageSource
 }
 
 /// Describes the application itself.
diff --git a/src/main.rs b/src/main.rs
index 83a22de..f5bdc5e 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -11,10 +11,13 @@ extern crate serde_derive;
 extern crate serde_json;
 extern crate toml;
 
+extern crate semver;
+
 mod assets;
 mod rest;
 mod config;
 mod installer;
+mod sources;
 
 use web_view::*;
 
@@ -44,8 +47,6 @@ fn main() {
     let size = (1024, 550);
     let resizable = false;
     let debug = true;
-    let init_cb = |_| {};
-    let userdata = ();
 
     run(
         &format!("{} Installer", app_name),
@@ -53,8 +54,8 @@ fn main() {
         Some(size),
         resizable,
         debug,
-        init_cb,
-        /* frontend_cb: */ |_, _, _| {},
-        userdata,
+        |_| {},
+        |_, _, _| {},
+        (),
     );
 }
diff --git a/src/rest.rs b/src/rest.rs
index e05702a..afdd361 100644
--- a/src/rest.rs
+++ b/src/rest.rs
@@ -36,7 +36,8 @@ struct FileSelection {
     path: Option<String>,
 }
 
-/// Encapsulates Hyper's state.
+/// Acts as a communication mechanism between the Hyper WebService and the rest of the
+/// application.
 pub struct WebServer {
     _handle: JoinHandle<()>,
     addr: SocketAddr,
@@ -85,6 +86,7 @@ impl WebServer {
     }
 }
 
+/// Holds internal state for Hyper
 struct WebService {
     framework: Arc<InstallerFramework>,
 }
@@ -95,6 +97,7 @@ impl Service for WebService {
     type Error = hyper::Error;
     type Future = FutureResult<Self::Response, Self::Error>;
 
+    /// HTTP request handler
     fn call(&self, req: Self::Request) -> Self::Future {
         future::ok(match (req.method(), req.path()) {
             // This endpoint should be usable directly from a <script> tag during loading.
diff --git a/src/sources/github/mod.rs b/src/sources/github/mod.rs
new file mode 100644
index 0000000..e0f1ba7
--- /dev/null
+++ b/src/sources/github/mod.rs
@@ -0,0 +1,19 @@
+/// github/mod.rs
+
+use sources::types::*;
+
+pub struct GithubReleases {
+
+}
+
+/// The configuration for this release.
+#[derive(Serialize, Deserialize)]
+struct GithubConfig {
+    repo : String
+}
+
+impl ReleaseSource for GithubReleases {
+    fn get_current_releases(&self, config: &TomlValue) -> Result<Vec<Release>, String> {
+        unimplemented!()
+    }
+}
diff --git a/src/sources/mod.rs b/src/sources/mod.rs
new file mode 100644
index 0000000..bbd9f18
--- /dev/null
+++ b/src/sources/mod.rs
@@ -0,0 +1,7 @@
+/// sources/mod.rs
+///
+/// Contains backends to various release distribution services.
+
+mod types;
+
+mod github;
\ No newline at end of file
diff --git a/src/sources/types.rs b/src/sources/types.rs
new file mode 100644
index 0000000..5d8f9a4
--- /dev/null
+++ b/src/sources/types.rs
@@ -0,0 +1,79 @@
+/// types.rs
+///
+/// Contains traits that should be implemented by sources, as well as corresponding types.
+
+use std::cmp::Ordering;
+
+use installer::InstallerFramework;
+
+pub use semver::Version as SemverVersion;
+
+pub use toml::value::Value as TomlValue;
+
+/// The version of an application.
+#[derive(Debug, Eq, PartialEq)]
+pub enum Version {
+    Semver(SemverVersion),
+    Integer(u64)
+}
+
+impl Version {
+    /// Coarses versions into semver versions. This will use a integer version as the major
+    /// field if required.
+    fn coarse_into_semver(&self) -> SemverVersion {
+        match self {
+            &Version::Semver(ref version) => version.to_owned(),
+            &Version::Integer(ref version) => SemverVersion::from((version.to_owned(),
+                                                                   0 as u64, 0 as u64))
+        }
+    }
+
+    /// Returns a new Version, backed by semver.
+    fn new_semver(version : SemverVersion) -> Version {
+        Version::Semver(version)
+    }
+
+    /// Returns a new Version, backed by a integer.
+    fn new_number(version : u64) -> Version {
+        Version::Integer(version)
+    }
+}
+
+impl PartialOrd for Version {
+    fn partial_cmp(&self, other: &Version) -> Option<Ordering> {
+        match self {
+            &Version::Semver(ref version) => {
+                match other {
+                    &Version::Semver(ref other_version) => Some(version.cmp(other_version)),
+                    _ => None
+                }
+            },
+            &Version::Integer(ref num) => {
+                match other {
+                    &Version::Integer(ref other_num) => Some(num.cmp(other_num)),
+                    _ => None
+                }
+            }
+        }
+    }
+}
+
+impl Ord for Version {
+    fn cmp(&self, other: &Self) -> Ordering {
+        self.coarse_into_semver().cmp(&other.coarse_into_semver())
+    }
+}
+
+/// A individual release of an application.
+#[derive(Debug)]
+pub struct Release {
+    pub version : Version,
+    pub files : Vec<String>
+}
+
+/// A source of releases.
+pub trait ReleaseSource {
+    /// Gets a list of the available releases from this source. Should cache internally
+    /// if possible using a mutex.
+    fn get_current_releases(&self, config : &TomlValue) -> Result<Vec<Release>, String>;
+}