I'm not sure that the Ed would be too happy about rival sites being publicised here!
However there aren't really that many anyway. The major US Q&A sites (such as Yahoo Answers and Answerbag) seem to be poorly moderated, resulting in them being full of trolls and spammers. (Yahoo Answers has a site that's nominally UK-based as well but it's actually part of the US site and has the same problems). Only Quora seems to be largely free of such problems.
StackExchange is particularly good for technology questions but has patchy content elsewhere.
There aren't any other genuinely UK-based sites similar to this one (to the best of my knowledge).
See here for some other general possibilities:
https://en.wikipedia.org/wiki/Comparison_of_Q%26A_sites
There are very few useable chat sites (as an alternative to Chatterbank) these days either. SagaZone was at one time a chat room aimed at the over-50s but it closed down due to its lack of moderation, leaving it full of trolls, spammers and (particularly) right-wing extremists.
There are several specialist crossword sites though, with Danword being my favourite but with others possibly preferring The Crossword Solver, CrosswordSolver.com or WordPlays.