package doMC NOT available for R version 3.0.0 warning in install.packages

If you want to install it for windows, here it how you can:

install.packages("doMC", repos="http://R-Forge.R-project.org")

I did it for R 3.2.3 version and it works well.

As Erdogan mentioned, it works for R 4.x.x versions as well.

I assume it's not available to you because you're using Windows. The doMC package has never been available on Windows because it depends on the mclapply function, before in the multicore package and now in parallel. I haven't heard of any issues with doMC in R 3.0.0.

The doSMP package was intended to be the Windows alternative to doMC. I believe it was eventually taken off CRAN because of problems building it on newer versions of GCC.

The doParallel and doSNOW packages are probably the most popular foreach backends available for Windows.