Sun 2 May 2021 07.00 EDT Isabelle Roughol was done with her day job at LinkedIn and was ready to start something of her own. She quit in early 2020 and launched Borderline, a podcast and newsletter aimed at “defiant global citizens”, and to help her build it she became an early user of a new online service: Substack. Substack has marketed itself aggressively to people such as Roughol as a new type of tech company, one that will let writers build their own brands and communities. The company offers software to help people set up free or paid-for newsletters and promises the people creating them that they can write what they want and that they own their own mailing list and can take it with them if they leave.