  Microscopes are vital pieces of equipment in much of biological research and
medical diagnostics. However, access to a microscope can represent a bottleneck
in research, especially in lower-income countries. `Smart' computer controlled
motorized microscopes, which can perform automated routines or acquire images
in a range of modalities are even more expensive and inaccessible. Developing
low-cost, open-source, smart microscopes enables more researchers to conceive
and execute optimized or more complex experiments. Here we present the
OpenFlexure Delta Stage, a 3D-printed microscope designed for researchers.
Powered by the OpenFlexure software stack, it is capable of performing
automated experiments. The design files and assembly instructions are freely
available under an open licence. Its intuitive and modular design -- along with
detailed documentation -- allows researchers to implement a variety of imaging
modes with ease. The versatility of this microscope is demonstrated by imaging
biological and non-biological samples (red blood cells with Plasmodium
parasites and colloidal particles in brightfield, epi-fluorescence, darkfield,
Rheinberg and differential phase contrast. We present the design strategy and
choice of tools to develop devices accessible to researchers from lower-income
countries, as well as the advantages of an open-source project in this context.
This microscope, having been open-source since its conception, has already been
built and tested by researchers around the world, promoting a community of
expertise and an environment of reproducibility in science.
