AI tool comparison
Cal.diy vs illumi
Which one should you ship with? Here is the side-by-side panel verdict, pricing read, reviewer split, and community vote comparison.
Productivity
Cal.diy
Cal.com, forked — all enterprise code removed, MIT licensed
50%
Panel ship
—
Community
Paid
Entry
Cal.diy is a community-maintained fork of Cal.com with all enterprise and commercial code stripped out — no Teams, no Organizations, no Insights, no SSO/SAML, and crucially, no license key required. Everything works out of the box under a pure MIT license. The goal is a truly self-hostable, zero-commercial-strings scheduling platform for individuals and small teams who don't need enterprise features but do need full data ownership. The technical stack is unchanged from Cal.com: Next.js, React, tRPC, Prisma ORM, and Tailwind CSS, with support for Google Calendar, Outlook, Daily.co video, email notifications, and standard event type booking flows. The project effectively resolves the "open core trap" by maintaining a clean split: if you want enterprise features, pay Cal.com. If you want a completely free, auditable, no-vendor-lock scheduling system, Cal.diy is the answer. With 41.5k stars (inherited from the Cal.com fork lineage), it has massive visibility. The maintainers are explicit that this is best suited for advanced self-hosters with server admin experience, not a one-click deploy for non-technical users. But for developers who want scheduling infrastructure without SaaS dependencies, it's arguably the cleanest option available.
Productivity
illumi
AI workspace that takes you from messy thinking to polished deliverable — and remembers the journey
75%
Panel ship
—
Community
Free
Entry
illumi is an AI visual workspace designed around one thesis: "execution got cheap overnight, but comprehension didn't keep up." The founders argue that modern AI tools accelerate output production but fragment the thinking process — each conversation starts fresh, context gets lost, and knowledge workers spend more time reconstructing mental models than doing actual work. The tool maintains session continuity across work phases: raw notes and messy thinking in early sessions are preserved and connected to the polished deliverables they eventually become. AI assists at each stage — synthesizing scattered notes into structured frameworks, drafting deliverables from frameworks, and flagging when new context contradicts earlier decisions. The workspace is designed to make the evolution of a project's thinking visible, not just its final outputs. illumi launched on Product Hunt on April 21, 2026 with 92 upvotes and sparked one of the more substantive discussions of the week — a thread titled "Is AI making knowledge work harder, not easier?" resonated strongly. A two-founder indie team built it. At this stage it's an early product with a clear POV, targeting knowledge workers who feel increasingly productive but increasingly confused about their own work.
Reviewer scorecard
“The open core model has always been a tension with Cal.com — features gated behind enterprise licensing in a supposedly open-source project. Cal.diy resolves that cleanly. The stack is familiar, the MIT license is genuine, and for anyone building a product that needs scheduling infrastructure, this is the right starting point.”
“The problem statement is accurate — I have a graveyard of ChatGPT conversations that led to good decisions I can no longer reconstruct. A tool that preserves the reasoning chain from messy brainstorm to shipping decision is worth trying. Whether illumi actually does that at v1 is the real question.”
“This is a maintenance burden in disguise. You're now responsible for keeping a large, complex Next.js codebase patched, secure, and up-to-date with upstream Cal.com changes — changes that may or may not land in the DIY fork on any predictable schedule. For most teams, Cal.com's free tier or Calendly is simply less operational overhead.”
“'Session continuity' and 'preserved thinking' are features that require deep integration into how you actually work — and most people won't restructure their workflow around a new tool unless it's dramatically better from day one. The 92 PH upvotes suggest interest, not retention. Come back in six months.”
“Scheduling is increasingly the integration surface AI agents use to take real-world actions — booking meetings, blocking time, managing availability across workflows. Having a fully controllable, self-hosted scheduling layer that AI agents can write to without SaaS rate limits or webhook restrictions is a genuine infrastructure advantage for agentic systems.”
“The 'cognitive overhead of AI' problem is real and growing. We're heading toward a world where AI-generated outputs vastly outnumber human-reviewed outputs — tools that make the thinking process durable and auditable aren't productivity luxuries, they're organizational infrastructure.”
“For content creators or solopreneurs who just need a Calendly replacement, self-hosting a full Next.js stack is overkill. The UX of the base Cal.com is fine but not exceptional, and the enterprise features you're losing (like organization-level insights) are actually useful for managing content calendar coordination across a team.”
“For content strategists and writers who live in the messy middle of multiple projects, a workspace that connects early ideation to final drafts without losing the 'why' behind every decision addresses a daily frustration. The visual approach feels right for how creative thinking actually works.”
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