Comicbrush is the latest addition to The Best Ways To Make Comic Strips Online.

It seems pretty accessible to English Language Learners.  There’s a gallery of created comic strips, but I couldn’t find anything objectionable with a quick look.  The site says it has pretty strict policy on inappropriate work, but I don’t know what amount of energy they put into enforcing it.

It uses some kind of point system to “purchase” some items, but many seem to be free and don’t require any actual money.