Back in 2012, I started teaching a mindfulness class to adults wanting to find a way to feel calmer and better able to manage their emotions. I used to hand out a list of useful websites from which people could download helpful recordings of guided meditations and other exercises. Well, since then, mindfulness has gone from fringe to mainstream. There are now numerous mobile apps that turn your phone into a pocket mindfulness coach and they can really help to keep you on track as you build a regular mindfulness practice. If you have an Apple watch, there is a useful app, called Breathe. For your smart phone, take a look at the following:

Headspace. One of the first really useful mindfulness apps, Headspace provides a free 10-day trial and an introductory course that takes only 10 minutes a day. If you decide to continue, you get access to much more content, including a program designed to help with relationships and personal health.
Calm. With Calm you can customize your experience by choosing the background scenery and noise that fits with your idea of a peaceful, soothing virtual retreat. It provides guided meditations, some of which are free while others require a subscription.
Buddhify. This app asks you what you are doing so that it can tailor a solo or guided meditation just for you. So if you are hanging around waiting for a friend or taking a quick break at work, Buddhify will create that peaceful moment.
Whil. If you prefer a mix of traditional meditation practices with video yoga sessions, then this app is for you. It can also pick a practice for you based on your mood, your intention, and the amount of time that you have to spare.
Insight Timer. This app allows you to choose your preferred interval time, ambient noise, and ending bell sound. It will also let you see in real time who else around the world is using the app to meditate.