This service allows you to connect a Mastodon account and a Twitter account and enable cross-posting between them. You can choose some options, such as if you want to post boosts, unlisted toots or replies.
Trunk allows you to mass-follow a bunch of people in order to get started with Mastodon or any other platform on the Fediverse. Mastodon is a free, open-source, decentralized microblogging network.