Hands-down winner for me is Radio Tray. Simple, works as advertised, and it's running pretty much 100% of the time my computer is on. It has never crashed. Very lightweight too, and the config file is simple enough that a quick glance at it in a text editor is all you need to make customizations faster than using the GUI preferences.

A very close second is the ext4 filesystem, but I don't know if this qualifies as software. I've done all kind of stupid things when formatting or unplugging drives and have never lost data. Full-disk encryption on everything and never a problem. SO reliable. I was doing a full backup to two separate drives at once, one external and one SATA internal. The power went out and I wasn't using a UPS. When the power came back on, everything was still fine but I was worried about data corruption so I plugged in yet another, my last good external drive with a known good copy of everything to compare against. Then the power went out again! I didn't even shout or curse, that's how mad I was. No data loss though, everything resumed from mid-backup and happily continued.