does the person find out why they were punished?

yes. they get a dm saying what happened, in which server, who did it and why. bans and kicks send it before they go, while fray can still reach them.

can i ban somebody who already left?

yes. ,ban takes an id, so it works on somebody who isn't in the server.

yes. ,warndecay set stops a warning counting after the number of days you pick.

yes. fray is free and there is no premium tier.

every action is a case: warns, timeouts, mutes, jails, kicks and bans each open a case you can look up by member or by number.
punish at a count: pick a warning count from 1 to 50 that kicks, bans or times somebody out the moment their active warnings reach it.
jail keeps their roles: jail takes every role and leaves only jailed. unjail hands them all back.
clears up after other bots: botclear deletes only what bots and webhooks said. people's messages are never touched.

every option is on the docs page.

does the person find out why they were punished?: yes. they get a dm saying what happened, in which server, who did it and why. bans and kicks send it before they go, while fray can still reach them.
can i ban somebody who already left?: yes. ,ban takes an id, so it works on somebody who isn't in the server.
can warnings expire?: yes. ,warndecay set stops a warning counting after the number of days you pick.
is it free?: yes. fray is free and there is no premium tier.

fray covers moderation, tickets, giveaways, reposts, roblox and ai, so a server doesn't need a separate bot for each of them.