You’re probably familiar with strangler figs, which grow on a host tree, often resulting in the eventual death of the host.
You’re probably less familiar with the strangler fig analogy as an OSS transformation or cutover model.
The concept is that there is a “host tree” (ie legacy system) that needs to be obsoleted and replaced, but it’s so dominant and integral (eg because of complex and/or meshed integrations) that a big-bang replacement is not viable (eg due to risk, costs, etc).
The strangler fig (ie new solution) is developed in parallel to the host tree and is progressively grown over time. Generally, it grows through step-wise enhancement / replacement. This approach is best suited to scenarios where there are lots of transaction types, fault types, process types, use-cases, etc that can be systematically switched from host to strangler.
This approach can also be used for product consolidation (ie multiple products consolidated into one).
Clever use of automated regression testing can help with this evolving cutover approach.
Edit: Without realising it, this pattern has some similarities with Strangler Fig applications as suggested by Martin Fowler back in his article from 2004.