LinkedIn is a social network for professionals. It is built using open source products. They sponsored many projects to open source. Here are the list of open source products used by LinkedIn.
Programming language: LinkedIn uses C++, Java, Scala, Python and Ruby.
Hadoop is a framework for running applications on large clusters built of commodity hardware. http://hadoop.apache.org/
Azkaban is simple batch scheduler for constructing and running Hadoop jobs or other offline processes. It is a workflow system for Hadoop which allows a program to be built out of small reusable pieces that need not know about one another. By declaring dependencies, you can control sequencing. http://sna-projects.com/azkaban/
Pig is a high-level data-flow language and execution framework for parallel computation. http://pig.apache.org/
Zoie is a real-time search and indexing system built on Apache Lucene. http://sna-projects.com/zoie/
Bobo is a Faceted Search implementation in Java, an extension of Apache Lucene. http://sna-projects.com/bobo/
Sensei is a distributed, elastic, realtime, searchable database. It is designed to handle billions of rows. http://sna-projects.com/sensei/
Read more: Best open source