Common Redist is used for "commonly redistributed" installers of other software the game relies on.

Like how sometimes when you install a game through steam and it also installs a Microsoft .net framework (because it needs that installed to run). In that case you'd the .net installer in the common redist folder. In this case, all those VCredist files.

OALinst is just an installer for OpenAL, a piece of audio processing software. A lot of games use it for handling positional audio, like something exploding to your left and behind you actually sounding like it exploded behind and to the left. Some games will also use it for more complicated audio things, like actually simulating sound echoes against the walls of a room and their material.