What are some alternatives?
When comparing SpeedFan and MailHog, you can also consider the following products
Open Hardware Monitor - Monitors temperature sensors, fan speeds, voltages, load and clock speeds, with optional graph.
Ruler - It's a screen ruler for Windows.
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.
Mailtrap.io - Mailtrap is a fake SMTP server for development teams to test, view and share emails sent from the development and staging environments without spamming real customers
iStat Menus - "An advanced Mac system monitor for your menubar."
DummySMTP - Simplify testing the email functionality of your application with a free DummySMTP inbox.