Acros is a manufacturer and distributor of trick bike equipment based in Renningen, just west of Stuttgart. In 2013 Acros employed Christoph Muthers and began manufacturing and selling his hydraulic gear system.

The story of Christoph Muthers and his amazing hydraulic derailleur system may go something like this:

• In the years before 2005 Christoph Muthers may have worked for Denk Engineering (which might both translate as ‘Think Engineering’ and have been run by one Peter Denk who had possibly worked for Scott and currently works with Cannondale). Denk Engineering were (are?) based in Freiburg, on the edge of the Black Forest and had a well publicised relationship with Scott - possibly developing frames and suspension systems for them.
• Some time around 2006 Christoph Muthers developed a rather beautiful (in a German kind of way) hydraulic derailleur system. Christoph applied for two related patents in August 2006. He almost certainly wins the prize for the derailleur system that contains the most ball bearing races (29 if you must ask). At this point, he appears to have left Denk Engineering and set up Muthers Fahrradkomponentenbau (which might translate roughly as Muthers’ Bicycle Component Works). From his web site, his company appears to have been based in Morscheid, in northern Germany, not far from the border with Luxembourg. The brand name that he used was 5rot.
• In 2011, after struggling to establish his system in the market, Christoph Muthers seems to have thrown in the towel and taken a job with Acros. At this point the 5rot brand disappeared and his hydraulic derailleur system reappeared as the Acros A-GE system, with the rear derailleur called Acros A-GE RD.
• In 2013 the Acros A-GE system was renamed the Acros A-GE MT system, with the MT denoting that it was for mountain bikes (with straight handlebars).
• A new system, called Acros A-GE RDA, was introduced for road bikes (with drop handlebars and STI style levers). The, short cage, Acros A-GE RDA derailleur had new, more curvaceous, zoomier, styling. I am not sure but I think that it was still 10-speed - and that it may never have been produced in volume.
• In 2015 the Acros A-GE MT system got a makeover, adotping the curvaceous styling of the A-GE RDA. The new Acros A-GE MT was upspecced to 11-speed and marketed as a 1X11 system.
• The 2016 catalogue, produced in late 2015 makes no mention of the Acros A-GE RDA.
• The last Acros Facebook post promoring the Acros A-GE system dates from 30th April 2016.
• An Acros Facebook post on 7th May 2018 refers to the Acros A-GE as being no longer made.

I am slightly confused about the various pulley cage lengths that were available. I believe:

• The very first mountain bike derailleurs (2011) had an 80mm cage.
• The range of mountain bike derailleurs was then expanded (possibly in 2012) to include 3 lengths: 60mm, 80mm and 100mm.
• The mountain bike range was then further expanded (possibly in 2013) to include 4 lengths: 60mm, 80mm, 90mm and 100mm.
• The road derailleur was only one length - possibly 80mm (although 60mm might seem more logical).
• When the new 11-speed mountain bike derailleur was introduced, it was only available in 90mm.