Not only can Agfa Scala be processed as negatives in a wide selection of conventional developers, Adox has recently released a Scala reversal kit that will allow you to produce B&W diapositives from nearly any B&W film, including Agfa and Adox branded Scala materials (this works best with films having a clear base, like Scala, Foma R100, and a few others).
Beyond that, I have personally processed B&W diapositives with a home process using Dektol as the first developer, a potassium dichromate and sulfuric acid bleach (hazardous material! I'd recommend potassium permanganate or copper sulfate as alternative bleaches), and HC-110 as second developer, with light exposure for reversal. I got good results with Tri-X (1990s vintage film, processed in 2005); I expect I'd have had better results with a film designed to be reversed.