Boot menu for Commodore 64 devices equipped with an Ultimate II+ cartridge. Version 2 is a full rebuild using the Oscar64 C compiler, replacing the earlier CC65-based version.

Version 2.1.0 adds a default boot slot with a configurable auto-boot timeout (great for auto-mounting a disk on power-on), and menu slots that only mount a disk and/or run a command without launching a program. Version 2.1.1 adds support for keeping the configuration and slot files on an SD card as well as USB storage. Version 2.2.0 adds automatic USB port rerouting: if a slot's disk image or REU file was saved against one USB port and the stick has since been moved to another, UBoot64 now finds it again at boot time instead of failing to boot.

Version 3.0.0 adds compatibility with Ultimate firmware 3.15 and later, including automatic UCI enabling from the cartridge and SoftIEC partition support (CMD-HD-style partitions, also usable on SD2IEC and CMD-HD hardware). The slot and config file format changed to record partition selection, hence the major version bump. Version 3.0.1 fixes a set of partition-related issues found during compatibility testing against firmware 3.15a and on real SD2IEC hardware, including a directory path bug that could cause a partition-based menu slot to fail to find its program.