diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..6dd29b7
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+bin/
\ No newline at end of file
diff --git a/runner.d b/runner.d
new file mode 100755
index 0000000..cf96109
--- /dev/null
+++ b/runner.d
@@ -0,0 +1,211 @@
+#!/usr/local/bin/rdmd
+
+/**
+ * Simple wrapper program for managing the various solutions. Each solution is
+ * defined as a single D source file in `src/sX.d`, where `X` is the number of
+ * the solution. All executables are placed in a `bin/` directory.
+ *
+ * This script can be executed standalone via `./runner.d`, provided that you
+ * have given the script the execution privilege (usually with `chmod +x runner.d`).
+ *
+ * It offers the following capabilities:
+ * - `./runner.d clean` removes all compiled binaries.
+ * - `./runner.d run [all | solution...]` Runs one or more solutions.
+ * - `./runner.d create <solutionName>` Creates a new solution source file.
+ */
+module runner;
+
+import std.stdio;
+import std.string;
+import std.process;
+import std.file;
+import std.path;
+import std.regex;
+import std.algorithm;
+import std.digest.md;
+import std.base64;
+
+int main(string[] args) {
+    if (args.length < 2) {
+        // By default, run the script with different behavior depending on what's available.
+        string[] runArgs = [];
+        string lastSolutionFilePath = buildPath("bin", "last-solution.txt");
+        if (exists(lastSolutionFilePath)) {
+            string solution = readText(lastSolutionFilePath).strip();
+            if (exists(buildPath("bin", solution)) && exists(buildPath("src", solution ~ ".d"))) {
+                writeln("Running the last solution that was previously ran.");
+                runArgs = [solution];
+            }
+        }
+        return run(runArgs);
+    } else {
+        string command = args[1].strip().toLower();
+        if (command == "clean") {
+            clean();
+            return 0;
+        } else if (command == "run") {
+            return run(args[2 .. $]);
+        } else if (command == "create") {
+            return create(args[2 .. $]);
+        } else {
+            writefln!"Unknown command: \"%s\". Should be one of: clean | run [solution...]"(command);
+            return 1;
+        }
+    }
+}
+
+/** 
+ * Removes all files from the `bin/` directory, which forces recompilation of
+ * any solutions.
+ */
+void clean() {
+    if (!exists("bin")) return;
+    foreach (entry; dirEntries("bin", SpanMode.shallow, false)) {
+        if (isFile(entry.name)) {
+            writefln!"Removing file %s"(entry.name);
+            std.file.remove(entry.name);
+        } else if (isDir(entry.name)) {
+            writefln!"Removing directory %s"(entry.name);
+            rmdirRecurse(entry.name);
+        }
+    }
+}
+
+/** 
+ * Runs one or more solutions, compiling them if needed.
+ * Params:
+ *   args = The arguments provided to this command.
+ * Returns: A program exit code.
+ */
+int run(string[] args) {
+    string[] solutionsToRun;
+    if (args.length == 0 || args[0].strip().toLower() == "all") {
+        auto r = ctRegex!(`^(s\d+)\.d$`);
+        foreach (entry; dirEntries("src", SpanMode.shallow, false)) {
+            auto c = matchFirst(baseName(entry.name), r);
+            if (c) solutionsToRun ~= c[1];
+        }
+    } else {
+        foreach (arg; args) {
+            string solutionName = arg;
+            if (!solutionName.startsWith("s")) solutionName = "s" ~ solutionName;
+            if (solutionName.endsWith(".d")) solutionName = solutionName[0 .. $ - 2];
+            string filePath = buildPath("src", solutionName ~ ".d");
+            if (!exists(filePath)) {
+                writefln!"The solution at %s doesn't exist."(filePath);
+                return 1;
+            }
+            solutionsToRun ~= solutionName;
+        }
+    }
+    if (solutionsToRun.length == 0) {
+        writeln("No solutions to run.");
+        return 0;
+    }
+    solutionsToRun.sort();
+    foreach (solution; solutionsToRun) {
+        bool canRun = true;
+        if (isSolutionRecompileNeeded(solution)) {
+            writefln!"Recompiling solution %s..."(solution);
+            int result = compileSolution(solution);
+            if (result != 0) canRun = false;
+        }
+        if (canRun) {
+            runSolution(solution);
+        }
+    }
+    return 0;
+}
+
+/** 
+ * Checks if a solution needs to be (re)compiled before it's run. This is the
+ * case when the executable doesn't exist, or the hash of the solution source
+ * doesn't match the hash of the current source.
+ * Params:
+ *   solution = The solution to check.
+ * Returns: True if we should recompile the solution.
+ */
+bool isSolutionRecompileNeeded(string solution) {
+    string solutionFilePath = buildPath("src", solution ~ ".d");
+    string hashFilePath = buildPath("bin", solution ~ "-hash.md5");
+    string executablePath = buildPath("bin", solution);
+    if (!exists(hashFilePath) || !exists(executablePath)) return true;
+    ubyte[] storedHash = Base64.decode(readText(hashFilePath).strip());
+    ubyte[16] currentHash = md5Of(readText(solutionFilePath));
+    return storedHash != currentHash;
+}
+
+/** 
+ * Compiles a solution using `dmd`, and includes an MD5 hash of the source in
+ * the `bin/` directory alongside the executable.
+ * Params:
+ *   solution = The solution to compile.
+ * Returns: 0 on success, or 1 on failure.
+ */
+int compileSolution(string solution) {
+    string solutionFilePath = buildPath("src", solution ~ ".d");
+    string hashFilePath = buildPath("bin", solution ~ "-hash.md5");
+    if (!exists("bin")) mkdir("bin");
+    ubyte[16] hash = md5Of(readText(solutionFilePath));
+    std.file.write(hashFilePath, Base64.encode(hash));
+    string utilFilePath = buildPath("src", "util.d");
+    string outputFilePath = buildPath("bin", solution);
+    string cmd = format!"dmd %s %s -inline -O -of=%s"(utilFilePath, solutionFilePath, outputFilePath);
+    auto result = executeShell(cmd);
+    if (result.status != 0) {
+        writefln!"Failed to compile solution %s, exit code %d:\n%s"(solution, result.status, result.output);
+        return 1;
+    }
+    return 0;
+}
+
+/** 
+ * Executes a solution, using this script's current working directory as the
+ * directory for the process, and inheriting all IO streams.
+ * Params:
+ *   solution = The solution to run.
+ */
+void runSolution(string solution) {
+    string processPath = buildPath("bin", solution);
+    writefln!"-----< %s >-----\n"(solution);
+    Pid pid = spawnProcess(processPath);
+    int result = wait(pid);
+    writefln!"\n-----< %s >-----\n"(solution);
+    if (result != 0) {
+        writefln!"Solution %s failed with exit code %d."(solution, result);
+    }
+    std.file.write(buildPath("bin", "last-solution.txt"), solution);
+}
+
+/** 
+ * Creates a new solution source file.
+ * Params:
+ *   args = The command line arguments.
+ * Returns: An exit code.
+ */
+int create(string[] args) {
+    if (args.length < 1) {
+        writeln("Missing required solution name.");
+        return 1;
+    }
+    string solution = args[0].strip().toLower();
+    auto r = ctRegex!(`^s\d+$`);
+    auto c = matchFirst(solution, r);
+    if (!c) {
+        writefln!"Solution name \"%s\" is not valid. Should be \"s\\d+\"."(solution);
+        return 1;
+    }
+    string filePath = buildPath("src", solution ~ ".d");
+    bool force = args.length >= 2 && args[1].strip().toLower() == "-f";
+    if (exists(filePath) && !force) {
+        writefln!"Solution \"%s\" already exists."(solution);
+        return 1;
+    }
+    File f = File(filePath, "w");
+    f.writefln!"module %s;"(solution);
+    f.writeln("import util;");
+    f.writeln();
+    f.writefln!"void main(string[] args) {\n    writeln(\"Hello from %s\");\n}"(solution);
+    f.close();
+    return 0;
+}
\ No newline at end of file
diff --git a/src/s1.d b/src/s1.d
new file mode 100644
index 0000000..a65bf2c
--- /dev/null
+++ b/src/s1.d
@@ -0,0 +1,6 @@
+module s1;
+import util;
+
+void main() {
+    writeln("Hello world!!");
+}
\ No newline at end of file
diff --git a/src/util.d b/src/util.d
new file mode 100644
index 0000000..bcf797c
--- /dev/null
+++ b/src/util.d
@@ -0,0 +1,12 @@
+/**
+ * Standard utilities that are included in any solution program.
+ */
+module util;
+
+public import std.stdio;
+public import std.file;
+public import std.string;
+public import std.algorithm;
+public import std.conv;
+public import std.path;
+public import std.uni;