Open source is an awkward fit for most launch directories, because their forms are built around a product with pricing and a signup. These nine take a repository as the thing itself. Show HN is first for the same reason as always: an audience that will read the code and tell you what is wrong with it, from a domain that has been indexing threads since 2007.
The rest divide by how much they will do for you. MCP Directory reads your repository and writes the entry, which is the least work available anywhere and also its own eligibility rule, since a private repo has nothing to read. DevPages syncs your star count weekly once a person has decided the tool belongs. DevTool.io and DevHunt want the tool to be genuinely developer-facing and will say so. Boilerplate Hunt and Open Source Boilerplates are for starter kits, with the second one running an explicit link swap on its Tools page. Startups.fm and LaunchBoard both take open source but are general boards, so read what their free lane actually returns before you spend an evening on either.
Across the 9 platforms on this list, median approval time is 4 days, 6 of 9 give dofollow backlinks, 6 are free to submit. Median domain rating: 41.