* Fractal (https://matrix.org/docs/projects/client/fractal.html) from the GNOME community (who just had a big hackathon in Strasbourg last week: https://wiki.gnome.org/action/login/Hackfests/Fractal2018). They're looking to add E2E and VoIP in the relatively near future.
* Nheko (https://matrix.org/docs/projects/client/nheko.html) - a very Telegram-looking Qt client, which has been in very steady progress for ages. They're actively working on E2E right now.
* Quaternion (https://matrix.org/docs/projects/client/quaternion.html) - a more IRC-like looking Qt/QML client, also in very active dev.
* Gomuks (https://matrix.org/docs/projects/client/gomuks.html) - this one's new; a really nice dedicated text-user-interface client written in Go - again, in very active dev.
Meanwhile we're also doing everything we can to improve Riot, but for desktop usage a native client will always beat an electron one :)