OldschoolFilter is a simple, extremely lightweight chat filter to remove the "[Player] joined channel." and "[Player] left channel." messages for the Oldschool channel, only.
The addon is completely Plug-n-Play and has absolutely no configuration. Turn it off via your favorite addon manager or the Character-screen addon list to disable it. Correspondingly, turn it on to re-enable it.
If you don't know what the Oldschool channel is, this addon probably isn't for you!
For the random passerbys: =)
The Oldschool channel is a channel named "Oldschool" located Horde-side on the Cenarion Circle-US realm, with the intent to gather players with the interest in older raids/dungeons/etc.