1) Use of plain Windows Media Encoder components. It is documented with samples in Windows Media Encoder SDK. Good for any high resolution streaming, but delay is too big for realtime chat (0.5-2 seconds at best). Modern Express Encoder SDK another option.
2) Microsoft Research ConferenceXP http://cct.cs.washington.edu/ Full featured conferencing API including application streaming. They too low level Windows Media coded filters and wrapped them into managed code. Works well. Easily customizable. Looks bit
3) Microsoft RTC Client up to version 1.3 - core of windows messenger.
pros: managed samples from Microsoft, good docs, reliable performance, freely redistributable, microsoft compatible (good) SIP stack included. Major conferencing vendors like Emblaze VCON based their solutions on it in some near past, not sure about
this days, but I know that Tandberg licensed Microsft's VC-1.
cons: version up to 1.3 support h261-h263 video only. modern version with support of VC-1(h264) codec does not allow direct serverless ip-ip connections. It does at require Microsoft Live Communications server. Newer version SDK does not cover well video