Risa is a German manufacturer founded by Rigk Sauer and based in Gross-Umstadt. They say they have three factories in Europe and I believe at least one of them is further east than Germany but I don't know exactly where. I know they also rebrand the products of other European makers as the Resonators are made in the Czech Republic by Amistar and some of the acoustic models are made in Portugal, (from the look of them I think by APC). 

They specialise in, and do make in their own factories, steel strung solid body electric Ukuleles, (they say, and probably are, the biggest manufacturer of this type of Ukulele in the World), and nylon strung solid body electric Ukuleles, (with undersaddle pickups). The steel strung ones come as Sopranos or Tenors, but with the solid nylon strung models there is also a Concert, (and I have seen both a Guitalele and a full size Guitar in the stick design too). 

I have seen some Models of Ukulele in the past that I have not seen elsewhere and may well have been the output of one of their own factories? but it appears now that all of their acoustic range is made for them by other people. 

I haven't seen a Risa branded Baritone, though there is a Uke Bass, (looks like APC), and apart from the 8 string Soprano electric bean that doubles up as an electric Mandolin I've not seen any string variations either. 

In 2014 they launched a range of Chinese made Ukulele branded as Koki'o. This range is aimed at the cheaper end of the market, starting with the colourful budget Sopranos and moving on to some better quality Minis through to Baritones and a Uke Bass in a large selection of laminate woods, plus some Resonators that I believe are made by Sinomusic and some plastic Sopranos that look like they come from the same factory as Woodi 

Risa nylon Ukulele strings are re-branded Worth strings but they do also sell specialist steel Ukulele strings G = 0.011" (0.026" for low G) ~ C = 0.017" ~ E = 0.013" ~ A = 0.010" if anyone wants to make their own set up.