You could call them the "Little 4," a play on the "Big 4" systems management companies: BMC, CA Technologies, HP, and IBM.
The Little 4 may be smaller in terms of their bottom lines, but in terms of systems management capabilities, there's nothing little about the open source offerings from Zenoss, Hyperic, GroundWork Open Source, and The OpenNMS Group.
This is a biosphere within the open source ecosystem that has seen a lot of flux in the past few years. In 2006, Zenoss was one of six vendors (the others being Ayamon, Emu Software, Qlusters, Symbiot, and Webmin) that launched the Open Management Consortium (OMC), "an effort to promote the adoption, development, and integration of systems and network management software based on open source and open standards technologies."
There is not much linking these companies together, other than a very healthy sense of coopetition. For the most part, the atmosphere in systems management land is friendly, though there are some skirmishes every once in a while.
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