Castan, at castan.ai, is operated by OCULI OMNIUM SRL. It describes itself as the AI that runs the back office of the company you own. It joins calls, chases invoices, keeps the books and remembers promises, and everything that leaves the company waits for your approval.
If you read that and thought of Nautis, you are right to compare them. Of all the products we've looked at, this is among the most similar in spirit: a morning note, a list of what slipped, agents that propose and people who approve. The architecture differs, and that decides who should buy which. Everything about Castan below comes from its site, read in October 2026. Its first-customer offer suggests it's early on. So is Nautis, which reached the public in July 2026.
Do you want to move your records, or leave them where they are?
This is the central question. Castan connects to the tools you already use, reads them, and builds one memory you can question. Its connections are read-only by design: Gmail and Calendar through Google's read-only scopes, Slack read scopes for channels its bot is invited to, and a restricted Stripe key. The one exception it names is Studio, which opens pull requests on repositories you choose. You can ask a first question within minutes of connecting one source.
Nautis asks you to work inside it. Tasks go on its task boards, deals in its pipelines, invoices are issued from its Invoices module, and email can run through MailBox. Setup through Liftoff takes about four minutes, yet the real work is moving your habits over. In exchange you drop several subscriptions and the data is structured, with an owner and a stage on everything. If you like your stack, Castan fits around it. If your stack is the problem, Nautis addresses that.
Nautis vs Castan, feature by feature
| Job | Castan | Nautis |
|---|---|---|
| Ask questions of company knowledge | Answers with citations across connected sources | Commodore answers from workspace data. Global search across modules |
| Morning note | Sent to your inbox before the first call. Nothing on a quiet day | 7:00 am briefing sorted into six groups, from Priorities to Runway |
| Weekly review | Monday review with receivables, promises and a drafted first step | Weekly digest on Monday mornings. Evening debrief on Voyage and Fleet |
| Calls | Own assistant joins Meet, Zoom or Teams. Recap to everyone about 2 minutes after | Transcripts arrive through a connected Fathom, Fireflies or Read.ai. Booking links built in |
| Invoices | Reads from Stripe. Writes reminders using the last thing the customer said | Issues PDF invoices, tracks payment, recurring invoices. Overdue items offer Send reminder |
| Financial view | P&L, burn, runway, bank-statement import | Startup Health, Financial Planner, Expenses. Not an accounting system |
| Custom agents | Plain-sentence agents on a schedule, 2 to 20 on paid plans | Routines: 5, 10 or 15 by plan, plus custom AI advisors |
| Build software | Studio writes pull requests to your GitHub and hosts waitlist sites | Not covered in the guides |
| Tasks and goals | Tracks promises. A dedicated task board is not listed | Task boards, Outcome Workflows, KPI tasks |
| Fundraising | Not listed | Investor directory, deal pipeline, readiness scoring and deck review, with a cap table from Voyage up |
| Documents and people | Lists, customer 360, team invites | Data rooms, DocSign, employee management, recruitment, team chat |
| Connect other tools | Gmail, Calendar, Slack, GitHub, Stripe. MCP server for AI tools, and it says it connects to any MCP server by address | 1,000+ apps through a managed catalog. MCP connector for Claude and ChatGPT |
| Approvals | Agents propose, and defaults ask | Agents propose in the Approval Center, and defaults ask |
Comparing price at four team sizes
Both vendors charge per company and not per seat, which makes this simpler than most comparisons. Castan plans differ by people, meeting hours, sources and runs, and it says every plan has the whole product. The table uses monthly list prices from October 2026. Castan's terms say paid plans bill per workspace, monthly, and its pricing page lists no annual option.
| People | Castan | What it includes | Nautis |
|---|---|---|---|
| Up to 3 | $0, or Founding at $29 | $0: 1 meeting hour, 2 sources. Founding: 5 hours, 3 sources | Launch, $49, up to 5 people |
| Up to 10 | Starter, $99 | 10 meeting hours, 4 sources | Voyage, $99 |
| Up to 25 | Growth, $299 | 40 meeting hours, 6 sources | Fleet, $129 |
| Up to 60 | Scale, $599 | 100 meeting hours, 8 sources | Above the 25-member cap |
Nautis costs more at the bottom and less at 25 people. Castan offers more room above that. The metering differs as well: Castan states that it has no meter on asking what your company knows, and limits meeting hours and Studio runs. Nautis meters AI use in credits, topping out at 2,600 a month on Fleet, and chat halts once the balance hits zero, pending a reset or a top-up. If your team would question the system constantly, that favours Castan. There is no $0 option on the Nautis side, only a 14-day trial.
One limit to note in Castan's $0 tier is 12 questions a day and the last 200 items per source, so treat it as a real sample and not a full run.
The late invoice, handled twice
Say you run a nine-person B2B startup, and a customer's $6,000 invoice is two weeks late. On last week's call they said payment was waiting on a revised contract clause.
- In Castan: the invoice reads as overdue from Stripe, and the promise from the call is already in memory, because its assistant was on the call. It drafts a reminder that mentions the clause. You press Send it, Change it or Not now. The strength here is context, and it needs Stripe and the call both connected.
- In Nautis: the invoice, issued from Nautis, turns overdue and lands in the 7:00 am briefing with Send reminder. Do it raises an approval card for you to accept or reject. Runway sits alongside it, so you see what the delay means in months. The call detail reaches it only if a transcription tool is connected. The Invoices module doesn't chase on its own, so someone has to act or set up an Invoice Chaser routine, which emails reminders on a schedule and asks first unless autonomy allows it.
On this exact case, we think Castan's published design is more impressive, because it joins the money to the conversation. Change the case to a Series A process with 40 investors and a data room, and Castan's pages have little to say while Nautis has a full module for it.
How each handles trust and data
Castan's security page is worth reading as a model of candor. It lists only what's in place today, including what it hasn't got yet: it says it has no named security attestations so far, and plans them for when a customer's procurement asks. It does report an independent CASA Tier 2 assessment. The app and database run in the EU, text sent to the model goes to Anthropic in the US under no-training terms, and members' answers exclude financial sources unless they are owners.
Nautis controls access through roles and per-module permissions, and every agent action is audit-logged, with deleting never automated. It doesn't claim any security certification either. If your buyer or board needs a specific attestation, ask both vendors directly. In the AI governance guide you can read how the Nautis controls work.
When Castan is the better pick
- You run a services or trade-style business that lives on calls, invoices and promises and has no plans to raise. Its demo revolves around orders, samples and shipping terms, and its language is about the company you own.
- You won't migrate anything. Read-only connections mean nothing changes in your stack.
- You want calls covered natively, with recaps sent to all participants and no separate notetaker bill.
- You want a website or code work included, since Studio files pull requests you can review and keep.
- You are between 26 and 60 people, or just want to start at $0.
When Nautis is the better pick
- You are raising or about to. Investor sourcing, pipeline, readiness checks, deck review, data rooms and cap table sit together. See Nautis for seed-stage startups.
- You need the system of record, not just a reader. Invoices, leads, tasks, signatures and employee records can all live here.
- You have 10 to 25 people on a tight budget. $129 against $299 at the top of that range.
- You want WhatsApp as a way in, though Nautis enables it workspace by workspace, and some don't have it yet.
The cost is breadth over depth, since a specialist will go further in any one module, and the effort of moving in. A half-filled workspace gives a thin briefing. Our 30-day rollout guide shows what that takes, and it may persuade you that Castan's lighter route suits you better.
FAQ
Should I move my tools in Nautis vs Castan?
With Castan you don't have to, because it reads your existing tools through read-only connections, joins calls and answers with citations. Nautis asks you to keep tasks, invoices, leads and investor deals inside it. Both propose actions and ask for approval by default.
How much does Castan cost?
Castan's October 2026 pricing runs from $0 for up to 3 people, through Founding at $29, Starter at $99 and Growth at $299, to Scale at $599 a month, flat per company. The first 20 customers get Growth at $199 a month for life. Extra Studio runs are $25 for a pack of 25 and extra meeting time is $39 for 10 hours, both one-time.
Does Nautis join calls like Castan?
Not with its own assistant, based on the guides. Connect Fathom, Fireflies or Read.ai and Nautis displays a recording's summary, action items and transcript, and those action items can feed the briefing. Castan's assistant joins Meet, Zoom and Teams directly.
Can Castan send email from my mailbox?
No. Its site says the Gmail connection is read-only and that it sends only its own mail: recaps, invitations, notices and approved invoice reminders. Nautis MailBox does let you read, reply and send from a connected mailbox.
Do Castan and Nautis both keep the books?
Castan says it keeps the books, with P&L, burn, runway and bank-statement import. Nautis isn't an accounting system and has no bookkeeping or tax filing. Check with your accountant what either output can replace before dropping existing software.
Disclosure: We make Nautis, so we have a stake in this comparison. It's based on published information, not a scored hands-on test. Spotted something out of date? Tell us and we will correct it.
Sources
- Castan: homepage and questions (checked Oct 31, 2026)
- Castan: pricing (checked Oct 31, 2026)
- Castan: security (checked Oct 31, 2026)
- Castan: terms (checked Oct 31, 2026)
- Castan: MCP server docs (checked Oct 31, 2026)