1.

Video websites, built in JAVA or PHP

2.

Community or social

3.

Flash player and other clients

Backend technologies:

1.

Search engines

2. .

hadoop

,

Big data and recommender system

3.

Distributed storage

4.

CDN+P2P

5.

Message engine

6.

Uploading system and auditing system

7.

Distributed transcoding engine

8.

Load balancing

9.

Image processing algorithm