I wrote Onno from scratch and I was the only one who worked at the source code. Yet there are are many people to whom I am indebted.
First, there is Fabien Letouzey and all the other people who contributed to the Fruit project. The study of the fruit sources was what initially motivated me to start chess programming. The algorithms were strikingly simple – at least for my scale – yet very effective. I was pleased with the source but yet I spotted many things that I wanted to do fundamentally differently. So I wrote a new engine from scratch. Many but not all of its algorithms are similar to those in Fruit; it would not have been possible to make progress so quickly without having the Fruit sources to look at. Onno's data structures and Onno's software design are however very different from Fruit and Onno does not contain any code from Fruit or another engine.
Onno uses a technique called "magic multiplication" for move generation. Thanks to everybody who contributed to it, among others Gerd Isenberg, Lasse Hansen, Pradu Kannan, and Tord Romstad.
Onno can use endgame tablebases from version 1-1-0 on. Many thanks to Eugene Nalimov and Andrew Kadatch for computing them and for their kind permission to use their access code. Also thanks to Robert Hyatt for his explanations on the state of tablebase module and for his permission to use lock.h.
Ron Murawski also contributed some ideas to my software.
Then there are the people at the internet chess fora. First of all those who administer the fora, especially the Winboard forum, but also those who discussed chess programming ideas on a very advanced level.
Many thanks also to Kai Tietz, who provided an alpha of a 64 bit version of the GNU compiler for Windows. He helped me to get it working (but finally I pefered a commercial compiler).
Then there are the beta testers who provided useful feedback. Graham Banks, Shaun Brewer, Olivier Deville, Werner Schüle, Charles Smith, Gerhard Sonnabend, Gabor Szots, and Wolfgang Battig run series of automated games and gave feedback on technical issues. Matthias Krämer looked intensively at the style of Onno and provided me detailed analyses.
Last but not least there is Clemens Duvenbeck who gave me an inexpensive way to put this website online.