Most of the setup work that needs to be done for specific CI systems is handled by the respective R client packages such as {circle}. These enable the repo on the CI system and ensure that deployment permissions are granted.
After everything has been set up, the rest of the work goes to {tic}.
In essence, tic::use_tic() is a wrapper for creating CI
YAML templates and setting up deployment on the CI systems which is
powered by the client packages.
Currently, the following CI client packages exist:
The client package for travis was archived in November 2020.
For Appveyor there is r-appveyor from Kirill Müller. This project makes it possible in the first place to run R checks on Appveyor but does not provide access to the Appveyor API and is not used by {tic} currently. Also, it does not come with automation for deployment setup. Appveyor support has been removed from {tic} in December 2020 due to a strong focus on GitHub Actions.
For GitHub Actions there is {ghactions} from Max Held which comes with functions helping to set up YAML templates and other convenience. It does not provide API access and is not used by {tic} currently.