UPDATE 3/5/25: I saw that this build is somehow still top 3 on [Limbo] 6 years later so I figured to do people a favor and update it.
Major changes: Helminth, arcanes and more of a focus on rift torrent.

Limbo, build-wise, is incredibly versatile in how he can be customized. Due to this, adjustments can easily be made to this build depending on preference. Need more duration, or less range? Easy to switch out.

In this build with the mods exactly as shown, it will provide excellent crowd control for a large space and for a long period of time. Our duration gives us 46 seconds on cataclysm which is more than enough, and our range is also very high to get [Rift Torrent] to apply to as many enemies as possible. Strength is used only to bolster [Rift Torrent].

[Rift Torrent] in this exact build will have a 68% damage bonus per enemy, which adds up very quickly with a lot of enemies inside the rift. As you kill the enemies it will decrease which is the major detriment of [Rift Torrent], so you will need to supplement with actually good weapon builds. [Rift Torrent] also stacks with Breach Surge, the helminth ability of [Wisp], which results in some major numbers. It needs to go over [Limbo]'s 1 because his other abilities are critical to the build.

[Primed Flow] is opted for instead of a lot of efficiency mods because of [Limbo]'s passive granting him 10 energy for each enemy he kills in the rift. [Streamline] is also in this build to counteract [Blind Rage] but if you like to live on the edge you can swap it out for duration or power strength.

The exilus mod may also be swapped. [Primed Sure Footed] is a popular choice, but ideally you won't be hit as [Limbo] in the first place (not to say it doesn't happen, it totally does). [Cunning Drift] is a good choice for more range and what I would recommend. It can be swapped based on player preference, though it may require forma.

This build is primarily used for open world content, excavation, interception and other gamemodes that require control over a large area. Also works very well in survival, especially SP. Remember to be cautious when bringing this build into corpus/corrupted missions, however: nullifiers will bring down cataclysm instantly upon contact. Also keep in mind that eximus units will be immune to stasis until you break their overguard--but their weapon attacks will be frozen and cannot hit you. They can only hit you through their energy attacks (the ones coded like warframe abilities).

ARCANES: Very versatile here.
Molt Augmented for more ability strength
Molt Efficiency for more duration
Arcane Aegis for survivability in a pinch
Arcane Strike if you like to melee a lot, just a personal favorite of mine.

You should never need energize. [Limbo] has no energy problems. Just hop in the rift and let your passive do the work.

ARCHON SHARDS:
Relatively versatile here. My setup is (all tauforged) 2 yellow, 3 red. Cast speed, parkour velocity (for utility), and 3 ability strength. You can pretty much do whatever you want here though and it isn't going to hurt, but I do recommend at least one cast speed since [Limbo]'s base cast speed is kind of low. If you want to forsake it though, it'll still work out fine because you can just cast your abilities from inside the rift where you are much less prone to damage.

FOCUS SCHOOL:
You won't need zenurik. I suggest naramon if you're into melee, or unairu to give yourself a source of armor strip. Otherwise this is mostly player preference.

ALTERNATE HELMINTH:
Silence if you really hate eximus.
Grouping abilities for easier time CCing (but the cataclysm is so big that this probably isn't necessary)
Roar/eclipse/[Xata] for weapon damage. I do not run these personally and I'm not really into spreadsheets so I don't know how these interact with rift surge but it can't hurt, right?

TIPS/TRICKS:
Start missions by running into the rift to start your energy [Regen].
Cast stasis and cataclysm from inside the rift so enemies can't hurt you during those long cast times.
If you double click stasis while it's on, it will go off and right back on very quickly if you need to refresh the timer.
Your operator can't go into the rift whatsoever, even under a cataclysm. This can be useful in certain situations. For example, if you have an arbitration drone inside your cataclysm (which is also immune to the rift status), you can go in your operator and kill it. Also works for hacking terminals.
If you're in a pinch and stasis is about to run out, assuming you have been consistently rift torrenting the guys in your cataclysm, you can drop cataclysm and stay in the normal plane. The enemies will be stuck in the rift and unable to hurt you.

This is a basic build for beginner and advanced [Limbo] players, but always make sure you communicate with your team about your ability use. Especially if you are casting rift surge a lot. Experiment with different utility mods while keeping the core ones and find out what suits your play style the most.