Technologic Systems (https://www.embeddedarm.com) offers a wide range of off-the-shelf, industrial-grade Single Board Computers, Computer-on-Modules, and Touch Panel PCs as well as custom hardware and software engineering services. Their boards are useful as OEM modules to integrate into your products as well as development and prototyping. Products can be purchased in single or bulk quantities (10k+), which can be customized to order starting at qty 100 to help bring down costs.
Most all of their boards come preloaded with Debian Linux, with the exception of a few newer products, like the TS-4900 CoM, which comes with Yocto and optionally Windows, Android, QNX, and Ubuntu/Slackware/Fedora/etc. Development can be done on the board thanks to the familiar software stack, including common Linux tools and interpreters. Most products, like the TS-7250-V2 SBC, TS-4740 CoM, or TS-7700 SBC, also come with an FPGA with unoccupied space available for the user to program. Simply copy your bitstream to root and the boot up scripts will automatically write it to the FPGA. Schematics, mechanical drawings, and source code are all freely available for download.