Add Cross-Claude MCP to community servers

[rblank9]

Adds Cross-Claude MCP — an MCP server that enables communication between multiple Claude instances through a shared message bus.

Features:

• 12 tools for messaging, channels, presence detection, and shared data
• Two modes: local (stdio + SQLite) and remote (Streamable HTTP + PostgreSQL)
• Works with Claude Code, Claude.ai, and Claude Desktop
• MIT licensed

Repository: https://github.com/rblank9/cross-claude-mcp

[olaservo]

Thanks for contributing to the MCP servers repo!

We've retired the third-party server list from the README in favor of the MCP Registry — see #3950 for context. The Official Integrations and Community Servers sections no longer exist in the README, so this PR no longer has a target.

Going forward, please publish your server to the MCP Registry using the quickstart guide:
https://github.com/modelcontextprotocol/registry/blob/main/docs/modelcontextprotocol-io/quickstart.mdx

That's where server discovery now happens. Thanks for building on MCP!

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Note: I'm working through the backlog with help from Claude Code to give everyone a prompt response.