The best replacement for playpen is crib.

The best alternatives to playpen are rated as following:
★★★★★  crib
★★  baby cot
★★  crate
★★  play yard
★★  cot
★★  pack n play
★  travel cot
★  bassinet
★  wooden crib
★  pack and play
  portacot
  crate training
  playard
  exersaucer
  lindam
  play pen

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

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



Google Trends

Scale is based on the average worldwide traffic of playpen in all years. Click on graph for more.
playpen
crib
baby cot