Former players can reactivate their accounts by logging in at PlayNC, while new players will need to first create a PlayNC account and then request a serial code through the Support page. The 2.92 GB game client can be found at FileShack.
"You'll need to activate your new account with a credit card number, but don't worry--that's just so we know who you are," explained developer NCsoft on the game's official site. "We will not charge your card for Tabula Rasa gameplay."
Along with being free, the formerly subscription-based MMO has recently seen several new content additions, including Earth, PvP Wargames, and Epic Caves of Donn.