The best replacement for clamshell is zagg.

The best alternatives to clamshell are rated as following:
★★★★★  zagg
★★★★  candybar
★★★★  bull pack
★★★★  flip phone
★★★  blister pack
★★  slider
★  candy bar
  blister

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

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



Google Trends

Scale is based on the average worldwide traffic of clamshell in all years. Click on graph for more.
clamshell
zagg
candybar