There's only one version of REAPER. One complete,
solid, full-featured digital audio workstation.
Your one-user, full-use license
includes up to two
major version numbers' worth of REAPER's famous frequent upgrades.
Purchasing a license now includes upgrades through REAPER 5.99.
REAPER 3.0 licenses purchased in 2009 are still valid for REAPER 4.x, and have seen over 100 free upgrades and counting.