Good to see the Appium 1.8.1 release, but I'm confused which one should I download?

3rd one is blockmap file.
Refer here for more details :https://github.com/electron-userland/electron-builder/issues/2851

4th one is Appium installer
This is what is called an NSIS-Web installer. What it does is it checks your environment (Windows OS version, 32 v. 64 bit, etc…) and then downloads the appropriate installer.

Refer here for more details: Windows Appium Desktop woes