What is a good open source program for monitoring various models of APC brand battery backups? I need notification of power loss, power restore, and imminent UPS shutdown (battery depleated). This latter is usually signaled by rapid series of beeps lasting about 30sec to a minute.

This needs to run in the background via cron or service, or monitoring program, not GUI. I don't particularly care about the software creating log files. What I need to for it to run something (e.g. a script I create) when these events occur.

What do you recommend? (please, only people who have installed/used such software respond. I know how to google)

Open - apcupsd
Closed - powerchute

Gee, having a bit of trouble assimilating your loquacious response. Probably too much detail for me to absorb all at once. What do you mean by "open"? What do you mean by "closed"? Does "open" mean "open source"? Does "closed" mean "proprietary"?

Yes.
Don't be a smart alec, it won't get you much help here.