A private channel per client
Invite a client straight into their channel from its People page. They get an email link and land in that channel, and that channel is all they see: not your other channels, not your team list, not anyone's email address.
Choose what they can do
Access is set per channel. Full access lets a guest chat and edit tasks and Docs. Chat only lets them talk while tasks and Docs stay view-only. Read only lets them follow along without posting.
Access that ends by itself
Set the last day a guest can use a channel, or the last day they can sign in at all. When the date passes, access switches off by itself, with nobody needing to remember.
Free, and clearly labelled
Guests don't count as paid users: every plan includes 5 guests for each paid user. Channels with guests in them are labelled, so your team always knows who can read along.