In open source, can there be more than one?

In the commercial market, multiple products is considered a healthy sign. The prevailing logic states that competition is a good thing, giving us the best possible product.

Vendors must position their products with a balance of different features and compatible operations. A word processor must provide some unique set of functions, but must provide some core set of functions to be considered a word processor. It must provide some compatibility to be considered useful to new customers (perhaps to convert their existing files). A bold, new approach to letter-writing, an approach that varies from the conventions of current products, will have a difficult time gaining acceptance. A word processor that performs the basic tasks of existing word processors, that is ten percent better at most things, and that offers a few new ideas, has a better chance of success. The commercial market allows for different, similar products.

The commercial market also has the risk of failure. Building a system on a product (say, a compiler or a  version control system) builds in the risk of that product. Companies fail, and products are discontinued (even when the vendor succeeds). The user must choose carefully from the available products.

In the open source ecosystem, the dynamics are different. Multiple products (or projects) are not viewed as a necessity. Consider the popular open source solutions for different tasks: Linux, LibreOffice, GIMP, gcc, SendMail, and NFS. There are competing offerings for these functions, but the "market" has settled on these projects. The chances of a project replacing the Linux kernel, or the GIMP package, are low. (Although not zero, as LibreOffice recently replaced OpenOffice.)

Open source is not monolithic, nor is it limited to single solutions. There are competing ideas for scripting languages (Perl, Python, Ruby) and editors (vi and Emacs). There are competing ideas for databases (MySQL and PostGres, not to mention CouchDB).

I think that it is harder for an open source project to remain independent from the lead project than it is for a commercial product to remain independent from the market leader.

In open source, your ideas (and source code) are available. A small project that is mostly compatible with a large project can be absorbed into the large project. To remain independent, a project must remain different in some core aspect. The languages Perl, Python, and Ruby are all different. The editors vi and Emacs are different. Because of their differences, they can continue to exist as independent projects.

For most software functions, I believe that there is a "Highlander effect": there can be only one. There will be one wildly popular kernel, one wildly popular office suite, one wildly popular C++ compiler.

When there are "competing" open source projects, they will either eventually merge or eventually distance themselves (as with the case of vi and Emacs).

A popular open source project can "absorb" other, similar open source projects.

This effect will give a degree of stability to the ecosystem. One can build systems on top of the popular solutions. A system built with Linux, GNU utilities, gcc, and Python will endure for many years.