[linuxydave]

ELK stack - Elasticsearch, Logstash, and Kibana. The whole stack is opensource :)

[oblio]

Interesting, but it's not a SaaS. It doesn't look like a direct rival to Splunk.

[linuxydave]

It is a direct rival to Splunk :) They do very similar things however IMHO Splunk is the better solution right now. There are LaaS companies that use ELK if you need a cloud solution - Loggly is the first one that springs to mind and I think another is LogSene.