The best replacement for blackboard is moodle.

The best alternatives to blackboard are rated as following:
★★★★★  moodle
★★★  whiteboard
★★★  angel
★★  webct
★★  canvas
★★  desire2learn
★★  chalkboard
★★  sakai
★  ecollege
★  green board
★  schoology
★  d2l
  canvas lms
  edmodo
  moodle comparison
  adobe connect
  chalkboard paint

Your alternative for blackboard is not listed? Suggest!
Speaking about blackboard, one probably shouldn't forget about chef.

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



Google Trends

Scale is based on the average worldwide traffic of blackboard in all years. Click on graph for more.
blackboard
moodle
whiteboard