Simple log to file for Unity3D apps. Designed for long running standalone application, logs a file per run in year / month folders.

Dbg.cs

using UnityEngine;
using System;
using System.Collections;
using System.Diagnostics;
using System.IO;

// Taken from here: http://www.thegameengineer.com/blog/2014/02/09/unity-11-logging/
// and adapted to my needs - per run log files, in year / month folders
// Steve Berrick <steve@berrick.net>

public class Dbg : MonoBehaviour
{
	//-------------------------------------------------------------------------------------------------------------------------
	public		string			LogFile = "log.txt";
	public		bool			EchoToConsole = true;
	public		bool			AddTimeStamp = true;

	//-------------------------------------------------------------------------------------------------------------------------
	private		StreamWriter	OutputStream;

	//-------------------------------------------------------------------------------------------------------------------------
	static Dbg Singleton = null;

	//-------------------------------------------------------------------------------------------------------------------------
	public static Dbg Instance {
		get { return Singleton; }
	}

	//-------------------------------------------------------------------------------------------------------------------------
	void Awake() {

		if (Singleton != null) {
			UnityEngine.Debug.LogError("Multiple Dbg Singletons exist!");
			return;
		}

		Singleton = this;

		// create year / month directories in the persistant data path
		string LogDirectory = Application.persistentDataPath + "/logs/" + System.DateTime.Now.ToString("yyyy") + "/" + System.DateTime.Now.ToString("MM");

		// actually create the directory if it doesnt exist
		Directory.CreateDirectory(LogDirectory);

		// set logfile name to be datestamped = new file for each run
		LogFile = LogDirectory + "/log_" + System.DateTime.Now.ToString("yyyyMMdd_HHmmss") + ".txt";

		// open stream
		OutputStream = new StreamWriter( LogFile, true );

	}

	//-------------------------------------------------------------------------------------------------------------------------
	void OnDestroy() {

		if ( OutputStream != null ) {
			OutputStream.Close();
			OutputStream = null;
		}

	}

	//-------------------------------------------------------------------------------------------------------------------------
	private void Write( string message ) {

		if ( AddTimeStamp ) {
			DateTime now = DateTime.Now;
			message = string.Format("[{0:H:mm:ss:ffff}] {1}", now, message );
		}

		if ( OutputStream != null ) {
			OutputStream.WriteLine( message );
			OutputStream.Flush();
		}

		if ( EchoToConsole ){
			UnityEngine.Debug.Log( message );
		}

	}

	//-------------------------------------------------------------------------------------------------------------------------
	public static void Log( string Message) {

		if ( Dbg.Instance != null ) {
			Dbg.Instance.Write( Message );
		} else {
			UnityEngine.Debug.Log( Message );
		}
	
	}

}

Nice work! perhaps an addition to this would be to check disk free and purge oldest logs when free disk is under a certain threshold.