Run by Austria’s Erste Bank, Brokerjet seems to be the main multimarket account offering online stock broking across several Eastern European countries (Croatia, Czech Republic, Hungary, Poland, Slovenia) that caters to English-speaking clients.
The firm also offers the smaller German regional exchanges (Berlin-Bremen, Dusseldorf, Hamburg, Hanover and Munich), as well as the main Frankfurt exchange and the smaller Stuttgart one. These are not usually provided by stock brokers outside Austria and Germany, although they are probably of limited interest to most investors. Fees seem reasonable compared to what you’ll pay for most Eastern European markets through traditional stock brokers.
The platform doesn’t seem to support multiple currencies in one trading account. So you’ll have to open separate deposits if you want to be able to settle deals in Poland directly in zloty, for example, and these may carry inactivity charges. But the currency conversion charge is a fairly low 0.25% if you don’t want to go to trouble of opening multiple currency accounts for settling the occasional trade in smaller markets.
I don’t have any direct user feedback, but found customer service was extremely fast and helpful when approaching them with questions about the account. Alternatives could be the Lithuanian firms Finasta and Orion Securities or the more costly Swissquote.