SpaceEngine

I usually search for them by selecting main sequence stars, then terras, if I want something more specific, I fiddle around with no. of stars, atmosphere, mass, and life.

Here's what I used for finding this planet moments ago. I didn't use life option. In this HIP system, there's 2 planets with life. And it's pretty easy to find terra planets using filters.

You cannot search for atmospheric composition...

I think that's a desired feature in future releases. I'm waiting to finish building my new PC, so I haven't tried 0.99 yet to see what improvements have been made in this area.  
I'd like to see it go as far as to be able to choose the levels of survivability. Like, short term, long term. Whether or not Humans could prevail or just get by...without eventually becoming unrecognizable as Humans after a few decades or so. lol

I use those exact parameters, like i did in my custom-made Carina III galaxy