diff --git a/lib/queue.class.js b/lib/queue.class.js
new file mode 100644
index 0000000..145d5b0
--- /dev/null
+++ b/lib/queue.class.js
@@ -0,0 +1,299 @@
+'use strict';
+
+const QUEUE_TIMEOUT = 'Metasync: Queue timed out';
+
+class Queue {
+  // Queue constructor
+  //   concurrency - <number>, asynchronous concurrency
+  constructor(concurrency) {
+    this.paused = false;
+    this.concurrency = concurrency;
+    this.waitTimeout = 0;
+    this.processTimeout = 0;
+    this.throttleCount = 0;
+    this.throttleInterval = 1000;
+    this.count = 0;
+    this.tasks = [];
+    this.waiting = [];
+    this.factors = {};
+    this.fifoMode = true;
+    this.roundRobinMode = false;
+    this.priorityMode = false;
+    this.onProcess = null;
+    this.onDone = null;
+    this.onSuccess = null;
+    this.onTimeout = null;
+    this.onFailure = null;
+    this.onDrain = null;
+  }
+
+  // Set wait before processing timeout
+  //   msec - <number>, wait timeout for single item
+  //
+  // Returns: <this>
+  wait(msec) {
+    this.waitTimeout = msec;
+    return this;
+  }
+
+  // Throttle to limit throughput
+  // Signature: count[, interval]
+  //   count - <number>, item count
+  //   interval - <number>, per interval, optional
+  //       default: 1000 msec
+  //
+  // Returns: <this>
+  throttle(count, interval = 1000) {
+    this.throttleCount = count;
+    this.throttleInterval = interval;
+    return this;
+  }
+
+  // Add item to queue
+  // Signature: item[, factor[, priority]]
+  //   item - <Object>, to be added
+  //   factor - <number> | <string>, type, source,
+  //       destination or path, optional
+  //   priority - <number>, optional
+  //
+  // Returns: <this>
+  add(item, factor = 0, priority = 0) {
+    if (this.priorityMode && !this.roundRobinMode) {
+      priority = factor;
+      factor = 0;
+    }
+    const task = [item, factor, priority];
+    const slot = this.count < this.concurrency;
+    if (!this.paused && slot && this.onProcess) {
+      this.next(task);
+      return this;
+    }
+    let tasks;
+    if (this.roundRobinMode) {
+      tasks = this.factors[factor];
+      if (!tasks) {
+        tasks = [];
+        this.factors[factor] = tasks;
+        this.waiting.push(tasks);
+      }
+    } else {
+      tasks = this.tasks;
+    }
+
+    if (this.fifoMode) tasks.push(task);
+    else tasks.unshift(task);
+
+    if (this.priorityMode) {
+      if (this.fifoMode) {
+        tasks.sort((a, b) => b[2] - a[2]);
+      } else {
+        tasks.sort((a, b) => a[2] - b[2]);
+      }
+    }
+    return this;
+  }
+
+  // Process next item
+  //   task - <Array>, next task [item, factor, priority]
+  //
+  // Returns: <this>
+  next(task) {
+    const item = task[0];
+    let timer;
+    this.count++;
+    if (this.processTimeout) {
+      timer = setTimeout(() => {
+        const err = new Error(QUEUE_TIMEOUT);
+        if (this.onTimeout) this.onTimeout(err);
+      }, this.processTimeout);
+    }
+    this.onProcess(item, (err, result) => {
+      if (this.onDone) this.onDone(err, result);
+      if (err) {
+        if (this.onFailure) this.onFailure(err);
+      } else if (this.onSuccess) {
+        this.onSuccess(result);
+      }
+      if (timer) {
+        clearTimeout(timer);
+        timer = null;
+      }
+      this.count--;
+      if (this.tasks.length > 0 || this.waiting.length > 0) {
+        this.takeNext();
+      } else if (this.count === 0 && this.onDrain) {
+        this.onDrain();
+      }
+    });
+    return this;
+  }
+
+  // Prepare next item for processing
+  //
+  // Returns: <this>
+  takeNext() {
+    if (this.paused || !this.onProcess) {
+      return this;
+    }
+    let tasks;
+    if (this.roundRobinMode) {
+      tasks = this.waiting.shift();
+      if (tasks.length > 1) {
+        this.waiting.push(tasks);
+      }
+    } else {
+      tasks = this.tasks;
+    }
+    const task = tasks.shift();
+    if (task) this.next(task);
+    return this;
+  }
+
+  // This function is not completely implemented yet
+  //
+  // Returns: <this>
+  pause() {
+    this.paused = true;
+    return this;
+  }
+
+  // Resume queue
+  // This function is not completely implemented yet
+  //
+  // Returns: <this>
+  resume() {
+    this.paused = false;
+    return this;
+  }
+
+  // Clear queue
+  //
+  // Returns: <this>
+  clear() {
+    this.count = 0;
+    this.tasks = [];
+    this.waiting = [];
+    this.factors = {};
+    return this;
+  }
+
+  // Set timeout interval and listener
+  //   msec - <number>, process timeout for single item
+  //   onTimeout - <Function>
+  //
+  // Returns: <this>
+  timeout(msec, onTimeout = null) {
+    this.processTimeout = msec;
+    if (onTimeout) this.onTimeout = onTimeout;
+    return this;
+  }
+
+  // Set processing function
+  //   fn - <Function>
+  //     item - <Object>
+  //     callback - <Function>
+  //       err - <Error> | <null>
+  //       result - <any>
+  //
+  // Returns: <this>
+  process(fn) {
+    this.onProcess = fn;
+    return this;
+  }
+
+  // Set listener on processing done
+  //   fn - <Function>, done listener
+  //     err - <Error> | <null>
+  //     result - <any>
+  //
+  // Returns: <this>
+  done(fn) {
+    this.onDone = fn;
+    return this;
+  }
+
+  // Set listener on processing success
+  //   listener - <Function>, on success
+  //     item - <any>
+  //
+  // Returns: <this>
+  success(listener) {
+    this.onSuccess = listener;
+    return this;
+  }
+
+  // Set listener on processing error
+  //   listener - <Function>, on failure
+  //     err - <Error> | <null>
+  //
+  // Returns: <this>
+  failure(listener) {
+    this.onFailure = listener;
+    return this;
+  }
+
+  // Set listener on drain Queue
+  //   listener - <Function>, on drain
+  //
+  // Returns: <this>
+  drain(listener) {
+    this.onDrain = listener;
+    return this;
+  }
+
+  // Switch to FIFO mode (default for Queue)
+  //
+  // Returns: <this>
+  fifo() {
+    this.fifoMode = true;
+    return this;
+  }
+
+  // Switch to LIFO mode
+  //
+  // Returns: <this>
+  lifo() {
+    this.fifoMode = false;
+    return this;
+  }
+
+  // Activate or deactivate priority mode
+  //   flag - <boolean>, default: true, false will
+  //       disable priority mode
+  //
+  // Returns: <this>
+  priority(flag = true) {
+    this.priorityMode = flag;
+    return this;
+  }
+
+  // Activate or deactivate round robin mode
+  //   flag - <boolean>, default: true, false will
+  //       disable roundRobin mode
+  //
+  // Returns: <this>
+  roundRobin(flag = true) {
+    this.roundRobinMode = flag;
+    return this;
+  }
+
+  // Pipe processed items to different queue
+  //   dest - <Queue>, destination queue
+  //
+  // Returns: <this>
+  pipe(dest) {
+    if (dest instanceof Queue) {
+      this.success((item) => void dest.add(item));
+    }
+    return this;
+  }
+}
+
+// Create Queue instance
+//   concurrency - <number>, simultaneous and
+//       asynchronously executing tasks
+//
+// Returns: <Queue>
+const queue = (concurrency) => new Queue(concurrency);
+
+module.exports = { queue, Queue };
diff --git a/lib/throttle.js b/lib/throttle.js
index b634039..c7dbda2 100644
--- a/lib/throttle.js
+++ b/lib/throttle.js
@@ -8,7 +8,7 @@
 //
 // Returns: <Function>
 const throttle = (timeout, fn, ...args) => {
-  let timer;
+  let timer = null;
   let wait = false;
 
   const execute = args
@@ -16,7 +16,7 @@ const throttle = (timeout, fn, ...args) => {
     : (...pars) => (pars ? fn(...pars) : fn());
 
   const delayed = (...pars) => {
-    timer = undefined;
+    timer = null;
     if (wait) execute(...pars);
   };
 
@@ -38,12 +38,15 @@ const throttle = (timeout, fn, ...args) => {
 //   fn - <Function>, to be debounced
 //   args - <Array>, arguments for fn, optional
 const debounce = (timeout, fn, ...args) => {
-  let timer;
+  let timer = null;
 
   const debounced = () => (args ? fn(...args) : fn());
 
   const wrapped = () => {
-    if (timer) clearTimeout(timer);
+    if (timer) {
+      clearTimeout(timer);
+      timer = null;
+    }
     timer = setTimeout(debounced, timeout);
   };
 
diff --git a/metasync.js b/metasync.js
index 571ebab..7d32bec 100644
--- a/metasync.js
+++ b/metasync.js
@@ -1,7 +1,7 @@
 'use strict';
 
 const common = require('@metarhia/common');
-const nodeVerion = common.between(process.version, 'v', '.');
+const nodeVersion = common.between(process.version, 'v', '.');
 
 const submodules = [
   'composition', // Unified abstraction
@@ -17,7 +17,7 @@ const submodules = [
   'throttle', // Throttling utilities
 ].map((path) => require('./lib/' + path));
 
-if (nodeVerion >= 10) {
+if (nodeVersion >= 10) {
   submodules.push(require('./lib/async-iterator'));
 }