Yahoo Bullet is a highly distributed framework designed for cloud multi-tenant data centers that let you run forward-looking queries. Bullet queries act on data flowing through the system after you submit the query.
In other words, you query data that will arrive, rather than data that has already arrived. Unusual for an open source project, Bullet also includes a visual user interface, so you're not necessarily restricted to command line or third party tools. And it also has a REST API for programmatic access.
As a query engine, Bullet was designed to be light weight, adding minimal overhead as you process streams. But there is some heavy lift involved in that the raw data, formatted as Avro files, must be parsed into columns that can then be hit with SQL queries that are placed over sliding time windows.
For now, Bullet is early stage technology, available as open source through GitHub. There's no vendor support and it's not part of any tool, so you're on your own with regard to managing and integrating it. Bullet competes in a very crowded landscape of log monitoring engines such as Splunk, Logstash/Elasticsearch, and others that provide near real-time capabilities.
The challenge for getting mindshare is proving the case that forward-looking queries provide the edge in knowing your customers through the digital log file footprints they leave.