As of my last knowledge update in September 2021, several health and fitness apps were popular and highly rated by users. Please note that the popularity of apps can change over time, so it’s a good idea to check the most recent app store rankings and reviews for up-to-date information. Here are some top health and fitness apps that were well-regarded:

1. MyFitnessPal: MyFitnessPal is a comprehensive app for tracking calories, exercise, and nutrition. It offers a vast database of foods and exercises, making it easy for users to manage their diet and fitness goals.
2. Fitbit: Fitbit is known for its wearable fitness trackers, but its app is also popular. It syncs with Fitbit devices and offers features like step tracking, sleep monitoring, and heart rate analysis.
3. Strava: Strava is a favorite among runners and cyclists. It tracks and analyzes workouts, provides route planning, and allows users to compete with others through segments.
4. Calm: Calm is a meditation and relaxation app that offers guided meditation sessions, sleep stories, and breathing exercises to reduce stress and improve mental well-being.
5. Nike Training Club: This app offers a wide range of guided workout routines, including strength training, cardio, yoga, and more. It’s suitable for users of all fitness levels.
6. Headspace: Headspace is another meditation and mindfulness app that helps users reduce stress, improve sleep, and build mental resilience through guided meditation and mindfulness exercises.
7. MapMyFitness: MapMyFitness by Under Armour tracks workouts such as running, walking, and cycling. It provides GPS routes, workout stats, and nutrition tracking.
8. Fitbod: Fitbod is a workout app that creates personalized strength-training routines based on your fitness goals, equipment availability, and workout history.
9. 7 Minute Workout: This app offers quick and effective seven-minute workout routines that can be done at home with no special equipment.
10. MyPlate by Livestrong: MyPlate is a calorie tracking app that helps users monitor their food intake, set weight loss goals, and track their progress.
11. Runtastic: Runtastic is a running and fitness tracking app that provides detailed statistics, GPS tracking, and audio feedback during workouts.
12. Yoga for Beginners: This app is designed for those new to yoga, offering step-by-step instructions for various yoga poses and routines.
13. FitRadio: FitRadio provides workout music playlists curated by professional DJs to keep you motivated during your workouts.
14. JEFIT: JEFIT is a strength training app that offers customizable workout plans, tracking features, and a large exercise database.
15. Lose It!: Lose It! is a weight loss app that helps users set and achieve weight loss goals by tracking calories, exercise, and nutrition.
16. StrongLifts 5×5: This app is geared toward those interested in strength training and the 5×5 workout routine, which focuses on compound lifts.
17. Fiit: Fiit is a fitness app that offers on-demand workout classes, including HIIT, strength training, and yoga, with a focus on interactive video sessions.
18. FitOn: FitOn offers a variety of workout videos, including cardio, strength, and yoga, led by celebrity trainers.
19. MySwimPro: Designed for swimmers, MySwimPro provides personalized swim training plans, tracking features, and technique videos.
20. Zwift: Zwift is an app designed for indoor cycling enthusiasts. It offers virtual cycling races and training sessions with interactive features.

Remember to choose the app that best aligns with your specific fitness goals and preferences. Always consult with a healthcare professional before starting a new fitness or diet program, especially if you have underlying health conditions or concerns.