Downloading nRF5x MDK for Keil4 8.11.1 from the developer's website was possible when we last checked. We cannot confirm if there is a free download of this software available. We recommend checking the downloaded files with any free antivirus.
The most popular versions of the nRF5x MDK for Keil4 are 8.5, 8.2 and 8.1. This free PC software is compatible with Windows XP/7/8/10/11 environment, 32-bit version. The software lies within Development Tools, more precisely IDE. The actual developer of the free program is Nordic Semiconductor.
From the developer:
The nRF51822 is a flexible multiprotocol SoC ideally suited for Bluetooth Smart (previously called Bluetooth low energy) and 2.4GHz ultra low-power wireless applications. nRF5x MDK for Keil4 is a set of APIs for nRF51822; this can be used along with Keil4 programming IDE.
You may want to check out more software, such as nRF5x-Command-Line-Tools or ARM, which might be similar to nRF5x MDK for Keil4.