Recommendation for free event monitoring software

Question

I'm seeking recommendations for free / open event monitoring tools. HPOV costs continue to multiply like so many wet gremlins, and we've had enough.

There are some interesting suggestions in this article and the subsequent comments, but before I set about trying many of these I'm sure you all have found a few that you like that may or may not be in this list. There is also this thread, but we're really shooting for a no-cost solution.

The primary requirements are:

1. Perform a basic ping test
2. Check the up-state of the SQL Server service.
3. Send an email alert if 1 or 2 fail.
4. Works as far back as Sql Server 2005 - present. (This is where PBM comes up a bit short)

Additional desired-not-required functionality would be:

1. Ability to pass a synthetic transaction, which if failed triggers an alert.
2. Ability to measure said transaction for duration, not just completion, and alert if a threshold is exceeded.
3. Alert on other measurable (logged) events.

Thanks much for any recommendations!

Edit: Currently investigating SpiceWorks