If you search "Micro Expressions" on the Apple App Store or Google Play, you will find several free apps.
While not exclusively micro expressions, this mobile app (available on iOS/Android) uses facial cues as part of its lie detection algorithm. micro expression training tool free
Dr. David Matsumoto, a student of Paul Ekman and a renowned expert in the field, runs Humintell. While their full courses are paid, they often offer a free demo version of their training tools. If you search "Micro Expressions" on the Apple