The best replacement for imu is ins.

The best alternatives to imu are rated as following:
★★★★★  ins
★★★★★  monash
★★★★  ahrs
★★★★  accelerometer
★★★★  icu
★★★  manipal
★★★  gross margin
★  mahsa
★  aimst
★  numed
★  ucsi
★  iru

Your alternative for imu is not listed? Suggest!
Speaking about imu, one probably shouldn't forget about kalman filter.

Other search terms related to imu and their ratings are:
★★★★★ kalman filter
You have in mind a companion for imu and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of imu in all years. Click on graph for more.
imu
ins
monash