The future.tools package is not, yet, on CRAN. In the meanwhile, it can be installed from the R Universe as:
options(repos = c("https://futureverse.r-universe.dev", getOption("repos"))) install.packages("future.tools")
To install the pre-release version that is available in Git branch develop on GitHub, use:
remotes::install_github("futureverse/future.tools", ref = "develop")
This will install the package from source.