What are some alternatives?
When comparing Ruler and Open Hardware Monitor, you can also consider the following products
MailHog - MailHog is an email testing tool inspired by MailCatcher, but easier to install.
SpeedFan - Hardware monitor for Windows that can access digital temperature sensors located on several 2-wire SMBus Serial Bus. Can access voltages and fan speeds and control fan speeds. Includes technical articles and docs.
Printix - Printix is a cloud-based print management platform.
iStat Menus - "An advanced Mac system monitor for your menubar."
LAN Messenger - LAN Messenger is a decentralized UDP IM-style chat client which supports usernames...
CPU-Z - CPU-Z is a freeware that gathers information on some of the main devices of your system : Processor name and number, codename, process, package, cache levels.