I'm not sure he is particularly active on HN but Rob Walling[1] is a solo entrepreneur managing at least a couple of Saas products: Hittail[2] (which he bought and then grow) and Drip[3]. He also conducts a podcast on Saas[4] and also organises a conference for self-funded startups[5]. In the past Patio11 spoke there too

[1] http://www.softwarebyrob.com/ [2] http://www.hittail.com/ [3] https://www.getdrip.com/ [4] http://www.startupsfortherestofus.com/ [5] http://www.microconf.com/ [3]