1.6.6 was an update for Team Fortress 2 Classic. It was released on January 15, 2015. It featured a few bug fixes. The patch notes are on the archived TF2C Wiki.
- Changed Tranquilizer damage, projectile speed and spread
- Fixed tf_weapon_criticals being at 0 giving constant crits
- Fixed Sniper headshots not working properly
- Fixed death notifications not showing the correct icons
I've also added a tf2c_random_weapons server variable. It's incredibly buggy right now, but still go ahead and try it.