Alas, Bayer Clinitest is no longer available. I purchased a stash of 200 tablets a few years ago that I continue to rely upon (On occasion, they show up on eBay at a premium price). As far as I know, an alternative for home winemakers is the Accuvin Residual Sugar Test....but I have no experience with that product. I would be interested in hearing about other alternatives that don't require a spectrophotometer or reagents with very limited shelf life.
It is not as accurate as hydrometry as mentioned above....but "good enough" to follow the progress of a fermentation. I have prepared a document describing the process and procedure: See http://www.moundtop.com/fermentation/RBRIX-ATC-Fermentation-Tables.pdf The refractometer approach's biggest problem is that it cannot be used to reliably to indicate dryness (end of fermentation). However, even a hydrometer comes up short here. As an amateur winemaker I rely upon Clinitest tablets to estimate the residual sugar level indicative of dryness. As always, there are many ways to skin this cat.